Circuits, Wiring, Relays, Switches
Maintenance FAQ for 7xx/9xx/90 Cars
Diagnosis Tips. For a superb introduction to basic automobile
electrical diagnosis using a digital multimeter and accessories, see Fluke
Corporationís website reference at http://www.fluke.com/application_notes/automotive/beatbook.asp?AGID=1&SID=103
Wiring Fault Diagnostic Tips.
[Tips from Import Car Magazine]
Wiring failures occur as open, shorted
or short-to-ground (grounded) circuits. An open circuit, obviously, is
a broken or disconnected wire. Shorted circuits occur when the insulation
between two wires fails. Grounded circuits occur when a bare wire is allowed
to touch the vehicleís powertrain, sheet metal or frame. As for narrowing
diagnostic probabilities, letís remember that:
1. Before wasting hours of expensive diagnostic
time, test all fuse circuits with a DVOM or approved test light. Remember
that fuses can fail without showing signs of an obvious burn-through. Since
a loose or corroded fuse connector may also cause many intermittent circuit
failures, thoroughly inspect and clean the fuse circuits before proceeding
with your diagnosis.
2. Most wiring failures occur at either
end of the wire as a bad connection. Although splice failures inside the
wiring harness are rare, some nameplates are notorious for splice failures.
Technical service bulletins (TSBs) and Internet sources offer valuable
insight to typical nameplate problems.
3. Corroded harness connections cause most
intermittent circuit failures. Simply unplugging the connector and applying
an electrically compatible corrosion inhibitor will repair most connector
4. When diagnosing intermittent failures,
remember that suspect turn signal flashers, fuses, bulbs and relays can
be replaced more cheaply than they can be diagnosed. When diagnosing an
intermittent lighting failure, for example, I always begin by cleaning
the bulb sockets and installing new bulbs. How much diagnostic time are
you willing to spend testing a $0.98 light bulb thatís nearing the end
of its practical service life?
5. Engine, computer and body ground connections
should be checked first, especially if the vehicle has recently visited
the collision repair shop.
6. Keep in mind that most electrical systems,
when left untouched, perform very reliably. When they do fail, the failure
will be predictable, such as a bad current or ground connection, blown
fuse and the like. Most predictable failures can be solved within a two-hour
7. On the other hand, the DIY mechanic
"short-testing" a cooling fan switch or fuel pump relay can create a multiple
failure with unpredictable consequences like burning a wire within a wiring
harness. Obvious tampering should always create a red flag... Electrical
"red flags" may include newly installed sound systems, electrical accessories,
trailer brakes, auxiliary lighting and the like...
8. Many circuits serve more than one accessory
or function. Years ago, for example, I found that a burned brake light
fuse was caused by a loose courtesy light in the ashtray. Without a good
magnetic short detector, the problem would have been difficult to solve
since a relationship between a brake light and ashtray light isnít immediately
logical or clear, to say the least. In other unlikely cases, Iíve found
an instrument cluster fuse that also supplies field current to the alternator.
The moral is, never rule out the effect of one circuit upon another...
10. In fact, avoid using test lights altogether.
When testing fuses, for example, I use an LED-type test light (available
from a major tool manufacturer) that indicates open or grounded fuse circuits
and voltage availability. This eliminates guesswork and protects ground-sensitive
electronic circuits like air bag sensors.
11. Use a professional DVOM with a min/max
voltage feature and alarm to test intermittent failures. The min/max feature
will record the highest voltage reached in the circuit and sound an alarm
each time a higher voltage is reached. For the technician working alone,
this feature is a real time saver, especially when performing a "wiggle"
test on an intermittent wiring problem. In the same sense, lab scopes are
particularly useful to find loose ground connections. During a wiggle or
vibration test, loose ground connections will show up as a voltage spike
in an otherwise zero-volt lab scope waveform.
12. Remember how hard it is to find the
trim screw driven through a wiring harness hidden underneath a headliner?
A good short detector will help you quickly locate concealed short-to-ground
circuits. For about 30 bucks, itís a great time saver for you and your
See the follwoing diagrams for fuse locations in 740/940 and some 760/all
740/940 Fuse Locations
960 Fuse Locations
Locations. See Michael Ponte's excellent illustrations below
to identify relays in 740/940 cars. To access relays, remove
the snap-on cover over the cigarette lighter, then remove the two screws
securing the storage box. Remove the box and you will see the relay
tray behind the fuses.
In 960 cars, the relays are in the same
location but mounted on a vertical relay board.
Relay Identification in UK 760 Model.
[Query] I need the relay identification on the relays which are located
on the side of the transmission tunnel under the plastic panel in the passenger
footwell compartment. These relays are labeled A,B,C,D,E,etc. No
disrespect ,but please do not refer to the ones in the compartment behind
the ashtray because I do not have that model. [Response: Steve]
In my 1990 760gle United Kingdom model the relays are A: main lighting(part);
B: motronic/jetronic relay; C: central locking relay; D: foglamp
relay; E: main lighting relay(part); F: bulb failure warning
relay (front); G: overdrive relay; J: power boost relay;
K: rear wiper delay relay; L:windscreenwiper delay relay; M: seat
belt warning relay. A, B, F, J, L, and M are permanently attached
to the board.
Fuel Pump Relay. The relay should not get hot even if the pump is drawing
too much current...until the excess current starts to kill the contacts.
Either way, a hot relay is a bad relay. There are three possible reasons
for a hot relay:
cold solder joint
All mean that a point in the relay has resistance
and when current flows through that point there will be a voltage drop
which means work is being done and that work manifests itself as heat (P
= E * I). Over time the bad joint gets worse due to the heat and maybe
heat cool cycles, the resistance goes up, the joint gets hotter, the voltage
at the pump goes down so it needs more current to do the same work so the
joint gets hotter, it gets worse, well you get the picture. At its worst
this kind of scenario can destroy a motor because the low voltage condition
causes a high current draw which over heats the motor. The relay may or
may not be fixable. I usually try to fix them and are often successful.
Note that Volvo released an improved relay, which has silver terminals,
to solve this problem. If the car's existing relay has copper-colored terminals,
replace it with the newer relay.
bad crimp joint
bad relay contacts
and Fuse Panel Removal. It is possible to pull the whole relay panel
out the front of its opening. Remove the plastic box (which also contains
the accessory socket) above it to facilitate this. There is an obvious
clip that you bend slightly to release the tray. Lift upward slightly,
then the tray slides rearward and out. The opening in the console is just
the right size--the tray does not need to be turned or twisted.The wire
umbilical attached to it is long enough to allow the panel to be pulled
out quite far. This is also how you can hook up accessories to the fuse
and relay connections under the panel. Use a good light so you can
Panel Base Replacement. My headlight relay got into a bad habit of
getting real hot. I had the same problem and after replacing the relay,
I replaced the plastic base. It's quite easy, get yourself a 1307160 ($2.89
CAD) and pull your relay/fuse tray out of there. After removing the relay,
flip the tray and remove each wire (tape the lug & mark the position).
You can usually coerce the crimp-on connectors out by bending the little
tab internal to each connector (with a small screwdriver). Once the relay
base is clear of wires, unclip and push it out. Install your new base and
re-install each wire in the proper position. I find that, using a knife,
you can "restore" the little tab on each crimp connector so that it "clicks-in"
when you re-install the connector in the base. It is vital to have firm
connectors or else they slide out when you push-in your relay! One additional
note... The base melts because there is resistance & arcing between
the crimp-on connector and the relay lug. There is quite a bit of current
going through there and you want to make sure that you have tight connections.
You can do that by "squeezing the gulls" of each crimp-on connector. Contacts
#30, 87 & 87b are the culprits (not sure if they are all used though).
My relay/fuse panel is all plastic. Double-check the part number of the
relay base by removing a relay and reading the part number in the center
of a "good" relay base.
Repair vs. Replacement. Here's a generic statement about your relay
(which I know nothing about) -- this statement displays my bias about the
(poor) quality of Bosch wave soldering. If you can pop the cover off the
relay, try resoldering all the connections on the circuit board before
you replace it. (After all, you have nothing to lose but a few minutes.)
The heavy connections that go to large components like the actual relay
may need a large soldering iron or gun, whereas the connections at smaller
components, such as transistors, should be reflowed using a smaller iron,
like a 25-Watt iron. If you're not comfortable soldering, find a friend
[Don Foster:] Over time (like 10
years), the solder used in production manufacturing tends to become crystallized
and cracks. The type of solder used in high-volume production is different
than that used in an electronics repair shop. The problem with the relays
is tiny, almost invisible microscopic cracks in the solder. These cracks
usually encircle one (or several) heavy connections, such as from the relay
or a main lug connector. Under a bright light, and using a magnifying
glass, inspect the soldered connections. Simply resoldering these circuit
board very often restores them to perfect performance, and it's a whole
lot better (and cheaper) than a $50-$100 replacement part. I have recovered
literally dozens of Bosch relays (OD, fuel pump, wipers) to perfect performance
this way at $0. In fact, I resoldered ALL the relays in my family's 6 Volvos
before a failure stranded us.
Window Switches. [Switches don't work] I can suggest one course of
action that helped to alleviate the situation, take apart the individual
window switches and clean them out. The switch pivot has a bit of oil or
grease on it and some of it gets on the ball bearing contacts, causing
dirt to get stuck and faulty contact points. The same may be true with
your child safety locks for the rear windows. It worked for mine, but I
think I need to clean the switch once more as it only operates correctly
80-90% of the time going down, and all the time going up. I was even thinking
of replacing the switch itself if that didn't work. No experience on the
power relays, though.
[Symptom: Window does not raise or lower.]
[Diagnosis:] Switch. These are fun to fix. Pull the switch assemblies
out of the door handle (two metal springs at front and back hold them in:
use a screwdriver to lever them out. Then pop the switch out (I usually
wind up doing them all as long as I'm there) and pry the side off the little
nipples so the cover comes off each switch. Be careful since there is a
spring in the rocker, you don't want to lose it. Take out the little metal
"lever" and use some very fine sandpaper to neaten up the contacts on the
lever and the contact points inside the switch. [Tip from John Yuristy]
. I wouldn`t use sandpaper or steel wool on contacts, some are just plated
and you will remove the good stuff.
[Response:Steve Ringlee] For a detailed
analysis of the window switches, take a look at Michael Ponte's analysis
Another solution is disassembling the switches (be careful in removing
them from the black plastic holders), de-oxidizing and cleaning them using
an electronic de-oxidizer such as DeOxIt from Caig Labs, then using a fine
Scotchguard nylon scrubber to burnish the contacts, and finally reassembling
them using Caig ProGold protective coating (very small quantities precisely
applied) on the contacts to prevent further dirt and oxidization from ruining
the contacts. Caveat: I have tried the "rebuild" approach on these
switches and found that it did not last that long; I ended up buying a
new driver's door switch from RPR for around $30 just to save more work.
Door Lock Failure. [Query:] There has been a failure of the door
locks on my 740 wagon. The tailgate unlocks with the drivers door but no
other function works. Do I need a new lock actuator or is there something
else to check? [Response:] There is a switch in the driver's
door that sends a signal to a relay mounted on the central relay panel.
The relay then sends power to all the lock motors (all doors except driver's
door). If some of the locks are operating and others are not, then you
have either a wiring problem or a ground connection problem. Either way,
the place to start is to remove the door panels on those doors that are
not working. Unplug the lock motors and check to make sure they operate
freely. If so, proceed to check the wiring with a multimeter - look for
bad ground connections, no power on lock/unlock leads when door switch
operated, etc. I expect that the three passenger doors are on one harness
and that the tailgate has a separate harness lead that comes from the relay.
So look for those points which are common to the three passenger doors.
Engine Wiring. [Early-80s to 1987 240 and 7xx cars:] Harness failure
often causes multiple symptoms such as rough idling, stalling, hesitation,
overall erratic performance and random misfiring. The symptoms may mimic
ignition or fuel injection trouble you've encountered on other cars. I
cannot address 240 vehicles newer than 87, the friends I help do not own
anything newer. In all the 240's I've seen there are several wires that
are "flaky": oil pressure; alternator wires and alternator dash signal;
knock sensor; water temp gauge; starter from ignition; starter to coil;
primary ignition wiring near the ignition coil; and on 7xx cars, harness
connectors in the right rear corner of the engine compartment below the
ignition coil. ALL the wires from the ECU do not show any signs of deterioration
in any of the harnesses we have opened up. Since the flaky set are wrapped
into the main harness to replace them means replace everything. At big
$$$ for Volvo & the service center. After getting nailed for the 85's
harness, I took preventive measures on my 83 and others until we find a
long down time to correct the problem. We replaced the alternator and the
oil pressure sending wires rerouting them around the right side of the
engine bay. We believe that if the alternator wire shorts to some other
wire that is where the big problems could occur. The alternator wire has
the potential to supply a constant 12+ volts to any of the others ( which
are to ground) and act as a heater wire inside the harness, getting hot
enough to melt all the others. In my 85 it was from the starter wire to
the alternator wire up by the dash connector and was caught before much
damage was done. Had it replaced by the dealer thinking insurance only
to find that insurance refuses to cover this problems in Volvo's. Cutting
open that harness revealed NO damage or deterioration to any other wires
in the harness except the above wires. Our solution: We reroute with new
wires to all of the above sensors. Best done with some other time consuming
task. To make it really easy we release the intake manifold. Takes two
of us about 3 hours to reroute all wires and replace the manifold. Tried
it first without releasing the manifold and it took 8 hours. I believe
Volvo could have created a replacement harness consisting of just these
wires but did not do so because of $$. Another is that if you catch the
problem soon enough no other wires will fry because of a short between
two of the bad wires. Wait too long and other wires will be damaged from
the heat of the short. Since this is probably about the time Volvo found
out about the problem, it looked to them like all the wires in the harness
[Quick preventative:] Watch the wires coming
from the connector directly under the windshield below the driver and the
oil pressure and alternator wires on the right front of the motor. These
are the first ones to go. If it starts reroute the alternator wire first
as this can cause the most damage if left in the harness. Then replace
the starter, then the coil wire as these have the next greatest potential
for damage. If you can, get the wires replaced before they cause other
damage, do so as the cost will come out of your pocket.
[1983-1987 7xx cars:] If you are referring
to the problem of wiring harness rot that affects the 83-87 models, it
usually affects the harness on the engine. On the LH cars, this usually
includes a fuel injection harness and a separate ignition system harness.
However, I have seen some deterioration of other underhood harnesses including
the wiring that goes to various lights (turn signals, corner markers, headlights,
[Advice on replacement:] The engine wiring
harness went bad on my 1983 240 Turbo (170,000). I noticed it first when
my starter would try to engage occasionally when I hit a bump or turned
a hard right. The wires up by the firewall on the left side of the car
were bare at the connector. I tried to separate and tape them, but that
did not work. I found out why when I replaced the harness. The harness
runs along the left side of the block, and EACH of the wires was completely
bare the majority of the length of the block!! As you know, depending on
which ones touched which, anything could happen. REPLACE the whole harness!!!!!!
Trying to patch it will only lead you into hours and hours of nightmares
both as you attempt to cob it together, and as soon as moisture gets in
your cheesy butt connectors and your gauges, idle, starter, etc go wacky!!!
Remember: My Volvo is Turbo. Although
a similar process, I can not speak directly on the naturally aspirated
version. The job took me (a former diesel mechanic but working with limited
tools on this job) 5 hours. I unbolted the intake and pulled it away from
the head. Of course to do this you will need an intake gasket. I recommend
you do this also, as to work around and under the intake would be treacherous.
With the intake pulled away, you can see straight down in there. You may
want to replace your flame trap when you are in there as you have a straight
shot at it. Any troublesome vacuum lines could easily be swapped out also.
The new Volvo harness is color coded exactly
as the original. (big advantage). It is also exactly correct in length.
(huge advantage). Just remove the old one, being careful at each connection
- temp sensors, alt, oil press, etc. are all very dry. You may have to
cut the old harness out in pieces as it is not pliable at all. Install
the new one by starting at firewall and working your way along the block
and around to the oil press and alternator. It is pretty self explanatory
really. Leave about 5 hours to do it. This sounds like a lot, but multiply
it times the hourly rate of your local shop, or the cost of burning up
a starter (and a tow) like I did, and you will have a little more incentive
to clear up some time on Saturday morning. No special tools. (May want
torque wrench for intake if you are REALLY particular). I shopped all over
and I purchased it from NILS SEFELDT Volvo in Houston Texas (281) 721-1600
(800) 468-0041 fro $230.22 and the gasket for $11.70. [Additional tips
from Dick:] My suggestion: do not remove the intake manifold on the
700 series. Remove AMM and hose to intake, idle speed motor and hoses,
also flame trap and oil trap. Label stuff carefully. Begin your rewire
from under the car, ie the oil pressure sender light, removing the old
stuff as you go. Your new harness has yellow bands indicating where the
clamps should be. Remove the harness from the AMM and replace with
new. You will have to remove the knock sensor wiring and mark it .
I think you get the picture. With the oil trap removed, you can clean it
and put a new O ring on it (leak source) and new flame trap. Other suggestion
is to remove the 3 plug ins on the passenger side and pull then through
and under the manifold along with the injector harness stuff.
Believe marking and labeling is extremely
important. I blew the brains out of a 240 by mixing up two similar 3-prong
connectors. Label the old harness too because you can always compare wire
colors in the connectors that are alike.
[More from a VCOA Wiring Clinic, courtesy
of the BrickBoard:]
Scope: The problem afflicts 200 and 700
series Volvos manufactured during the period 1983-1987 [Note: several commentators
would also include the 1981 & '82 models of 240 series.]. The problem
has also appeared in other vehicles manufactured during the same period
with Bosch electrical systems. Owners of all vehicles manufactured with
Bosch electrical systems during the period should inspect the engine wiring
harness. Anyone considering purchase of such a vehicle should inspect the
engine wiring harness if the harness is the original.
Presentation of problem: Disintegrating
insulation on wires exposed to high temperatures for long periods (10 years
Symptoms: All vehicles within scope are
vulnerable to the problem. Close inspection of the engine wiring harness
will reveal the problem before it causes short circuits. If a vehicle within
scope exhibits drivability problems that are intermittent and cannot be
otherwise diagnosed, short circuits in wiring harness caused by deteriorating
insulation may be the cause.
Inspection: Use a strong light source and
check wiring, paying particular attention to wiring passing close to high
heat sources. High heat sources include intake manifold, exhaust manifold,
turbocharger, block, firewall.
Common locations presenting problem: B23:
firewall near main connector, alternator, intake manifold. B230: ground
wires on intake manifold, oil pressure sender, water temperature sensor
on block. B28/280: no engines were available for inspection.
Temporary solutions: liquid electrical
tape, applied in several coats over several hours, good between -20 and
255 degrees F; shrink-fit insulation, applied with heat gun or torch, good
past 400 degrees F, but hard to fit correctly over end connectors; spliced
wiring, recommended by some Swedishbricks and SAAB list members as the
most nearly permanent fix that does not require a new harness. Standard
electrical tape is at best a one-month reprieve. Any solution short of
lasts no more than a few months.
Permanent solution: new wiring harness,
cost ranges between $250 and $350 (US). VCOA has been successful in persuading
Volvo to lower the price of its wiring harnesses for vehicles within scope,
and current price range quoted above reflects those reductions. Prices
have been cut from 33%-50% from previous levels (Example: old price of
engine harness for B230FT engine was approximately $500, now reduced to
$270). Dealers who offer club discounts will add their standard discount
to the current prices. It is absolutely critical that you order the correct
harness. Very difficult to do when there are 3-4 variants out there, yet
little way to tell the harnesses/engine applications apart.
Workability: Owners who prefer to have
a mechanic install the new wiring harness can expect to pay 4-6 hours of
shop time for the job. Owners who prefer to do the job themselves should
set aside one or two days. For the B230 engine, it is recommended that
the owner have all vacuum hoses replaced at the same time, as well as fuel
injector seals. In addition, performing the job on the B230 engine involves
removal of the intake manifold and air intake valve, and so requires replacement
of the intake manifold gasket and the air intake valve gasket. Owners who
have replaced wiring harnesses of B23 and B280 engines may wish to offer
advice on other maintenance that should be performed at the same time,
as well as other parts (besides the wiring harness) that may be required.
Dielectric grease for multi-pin connectors, as well as an oxidation inhibitor
for single connection points to aluminum ground, are recommended. Do not
interchange the two, as dielectric grease is an insulator, while oxidation
inhibitor is a conductor.
Picture References. Check
for visual images and instructions for
wiring harness replacement and other maintenance items.
Chassis Grounds. [Query:] What do I have to do to keep
the grounds in my chassis circuits in good condition? [Response 1:
Steve Ringlee] This is tough to do without the pictures in the Volvo OEM
wiring diagram book (the best $25 I've ever spent, by the way) but here
are the grounds for my 1990 745:
These grounds, if corroded, can play havoc
with your car's electrical system. A lot of the problems brought up in
both Brickboard and Swedishbricks forums relate to faulty ground connections.
It pays, especially for those in wet or salty climates, to clean and de-oxidize
the ground connections (DeOxIt from Caig Tools is great, at electronic
stores) then coat them with OxGard conductive paste (get it at Home Depot)
which is designed to protect electrical connections where conductivity
is important and shorts across circuit connectors are not a problem.
Battery chassis near the battery: often
[Response 2: Don Willson] One ground
connection you missed Steve. Though it has nothing to do with air bags
it will cause major running problems. That is the injector ground wires.
Just cleaning them and tightening the bolt is not enough. The wire must
be soldered to the crimp lug. The internal resistance of this crimp increases
until injectors start to missfire, the O2 sensor sees too much oxygen
and feeds the engine much too much fuel. Mileage drops to 10 mpg
with smoke and no power.
Engine main ground under the p/s pump
(typically OK because of oil coating)
Right auxiliary chassis ground (behind
right headlamp): frequently corroded
Left auxiliary chassis ground (behind
left headlamp): also usually corroded
Inside left A-pillar: underneath the trim
panel by the bottom front left door hinge;
Inside right A-pillar: just beneath the
engine computer by the right front door pillar; this is important since
so many functions ground here and humidity/salt can affect it from the
Left and right taillight grounds
On the right console between the seats:
not a problem
Courtesy lamp ground above the left B-pillar;
not a problem
Fuel pump and sensor ground next to sending
unit on fuel tank
SRS ground beneath the driver's seat next
to the crash sensor. It goes without saying that if you are going to touch
this, you need to disconnect the battery negative and wait some time for
any charge to dissipate from the crash sensor.
For a good overall discussion of Volvo
electrical system grounds, see the article ďVolvo Electrical System Service:
In Search of Good GroundsĒ, Bob Kraft, ImportCar magazine, December 1997
their searchable archive for ImportCar Magazine.)
vs. Conductive Grease to Protect Connectors and Grounds. [Query:] You
have repeatedly recommended the application of dielectric grease to underhood
wire connections. Isn't the insulating property of such grease counter
to the goal of IMPROVING the integrity of electrical connections? I would
think that a conductive paste (such as Eastwood's Kopr-Shield) would be
better. The only potential downside I can think of is that sloppy application
could cause short circuits, but care and common sense should preclude this.
[Response:] This is a good question and one that I have received several
times. Yes, it is true that the dielectric grease is non-conductive. However,
in the context of connections that carry voltages larger than 1 volt, the
grease will not result in a bad connection. The male and female connectors
will wipe enough of the grease off at the mating surface so that the electricity
will flow just fine. The important part is that there is no chance of the
grease creating a conductive path between adjacent terminals in a multi-terminal
connector. The main purpose of the grease is to seal the terminals against
oxidation which creates a high resistance barrier and moisture and dirt
which can result in shorts and ground paths.
It is important to note that on all Volvos,
the Oxygen sensor signal lead carries a very low voltage (0.2v - 0.8v)
and the dielectric grease must NOT be used on this lead as it will interfere
with the signal voltage.
For the GROUND connections - especially
those in the engine compartment where the ground leads are fastened to
aluminum surfaces like the intake manifold, I recommend using one of the
conductive greases like OxGuard. These are found at electrical supply houses
and are typically used by electricians to treat the end of aluminum electrical
cables to prevent the very high resistance aluminum oxide from forming
at connections - this was a common cause of house fires. The same high
resistance oxide plays havoc with engine management system signal voltages.
You can eliminate the problem by cleaning the aluminum surfaces and treating
with the conductive grease. Also note that many of the spade type crimp
on terminals that are available are made of aluminum. It is very difficult
to find copper ones. [Note: see also the note on greasing connectors under
Engine Tune, Performance.] DON'T use OxGuard on engine or chassis electrical
connectors or sensors.
Board and Contact Repair. [Tips from Joe Ward] My rear
taillight has been blowing the bulb rather frequently. Upon a closer inspection
I noticed it had worn the copper trace where the lamp holder contacts the
copper trace. I removed lamp holder, lightly sanded copper trace areas
with some 600 grit, cleaned with alcohol, applied a thin film of conductive
epoxy on all three copper traces and let dry overnight. Next morning it
was hard as rock and conductive! This product was found at a local
electronics supplier (it was near the check-out counter and it occurred
to me this would be a good product to try before replacing). Product is
used for field repairs for circuit boards that have cracked or broken traces
and soldering not available. Cost ~8.00 for tube but it didn't take much.
[Tip from JohnB] I had a similar problem with the plastic/copper
circuit board below the steering wheel on my Saab. So I sanded the copper
circuit and placed about 5-6 strands of copper from some 12-gauge multi-strand
twisted together and flattened onto the copper on the plastic and using
a 350w Weller soldering gun and electronic rosin core solder, just flashed
the copper/wires together
Windows Operate in OFF. 1986 740: I just noticed that my power windows
work without the key in the ignition. [Response:] a stuck relay would do
that. Either that or there's a hot short at the relay socket or in the
wiring between the relay and the ignition switch. Should be leftmost relay
in the front row. It also powers the electric radiator fan, so given a
hot engine on a hot day it too could run when the key is out. A hot short
between the relay and the fan thermostat would also enable the power windows.
Try tapping on the relay to see if that doesn't at least make a temporary
difference. If that helps then you may be able to salvage the relay by
opening it and using contact cleaner. If not, then pull the relay anyway
and inspect socket for evidence of shorting. After that it's either try
a new relay or start tracing with a multimeter.
Run Hot. 87 740 B230F 120,000 miles. Problems with the 740 fuel pump
and headlight relays are well documented. Volvo has a tech. bulletin that
recommends replacement of the relays and the sockets, which have both been
done to my car before I purchased it. Driving today, I put my finger on
the fuel pump relay and it was darn warm. I could just hold my finger on
it - any hotter and I wouldn't be able to. Is this normal/acceptable? If
no, what's the fix (another relay??). [Response:] Relays on Volvos run
hot. That's why I drill holes in the covers. You must first remove the
circuit board to drill the cover. On overdrive relays, I have never had
to replace a relay with holes in it, it seems to help a lot. I have also
run cooling to the relay/fuse board from the crotch cooler port, so when
the A/C is on, it blows cool air on the board via hose. It may help and
can't hurt. [Another:] I've seen several instances on 740s of excessive
contact resistance at the fuel pump relay connector. This causes overheating
and melting of the spade connectors and plastic socket. It probably wouldn't
hurt to examine the male spade connectors and socket for signs of high
resistance and overheating (discoloration of metal, melted or burned plastic).
[Another:] Your description of the innards of the fuel pump relay sounds
right.... the wires from the solenoid coils to the PCB are small and fragile
-- but I've never experienced them breaking (at least, breaking from vibration).
Because they're fragile, fingers off! Soldering the PCB is done on the
other side from the components. You'll notice the component leads (including
the fine wires) stick through and are soldered to so-called "traces". These
traces are copper, but are usually completely covered by solder so have
a silvery color. You'll also see where larger tangs stick through and are
soldered -- these are the heavy-current leads from the relay contacts as
well as the relay connectors.
I usually solder the heavy connections
using a soldering gun (but carefully, because these deliver a lot of heat
quickly, and can damage a PCB). The smaller solder connections are best
done with a small 25-Watt iron. Of course, you must use electronic solder,
not plumbing solder (which contains an acid-based flux).
Discharge. See the "Starting"
section for more information.
Electrical Failure: Ignition Switch Bad. [Query:] After
stopping our '90 745T the ABS light came on, the blinkers did not work,
along with the power windows. Wife managed to get home and call me at work.
My first reaction was, of course, a fuse. But when I got home and started
up the car, everything was fine, along with the fuses. Any ideas on a solution
to my quandary? [Response: Abe Crombie] The electrical switch behind
ignition lock is almost certainly the culprit. You can test for this by
starting car and then turn key a few degrees either way and see if you
can't duplicate what your wife observed. The switch has the spring in it
that returns the key to run position after you go to the starter position
and it can weaken or wear. The switch is easy to change and is readily
available through a good parts supplier.
Control Surges: Worn Servo. [Query:] What is the fix for
surging with the cruise control ON. It tends to fluctuate 2-4 mph in level
driving conditions. Real annoying. [Response: Abe Crombie] Look closely
at the servo on the throttle housing that tugs the cable wrapped around
the throttle spool. This can get a hole worn in it and the vacuum level
that keeps throttle positioned evenly is impossible to maintain.
FAQ for 7xx/9xx/90 Cars
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