Electrical: Circuits, Wiring, Relays, Switches                                         FAQ Home
 Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Version 5.0
 
Electrical Diagnosis Tips

Fuse Locations

Relay Locations

Hot Fuel Pump Relay

Relay and Fuse Panel Removal

Relay/Fuse Panel Base Replacement

Relay Repair vs. Replacement

Power Window Switches

Power Door Lock Failure

Baked Engine Wiring

Maintaining Chassis Grounds

Dielectric vs. Conductive Grease to Protect Connectors and Grounds

Circuit Board and Contact Repair

Power Windows Operate in OFF

Relays Run Hot

Slow Battery Discharge

Multiple Electrical Failure: Ignition Switch Bad

Cruise Control Surges: Worn Servo


Electrical 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]
DIAGNOSTIC THOUGHTS
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 failures.

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 time block.

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 customer alike.



Fuse Locations.  See the follwoing diagrams for fuse locations in 740/940 and some 760/all 960 cars:

                740/940 Fuse Locations                        960 Fuse Locations


Relay 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.


Hot 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: 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.

Relay 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 see well.

Relay/Fuse 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.

Relay 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 who is.

[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.


Power 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 at http://www.mikeponte.com/volvo/pwin.htm.  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.


Power 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.

Baked 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 are bad.

[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, etc.

[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 or more).

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.

Solutions:
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 splicing 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 out http://www.homestead.com/volvo2/harness.html
for visual images and instructions for wiring harness replacement and other maintenance items.



Maintaining 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.

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 at http://www.underhoodservice.com/ (see their searchable archive for ImportCar Magazine.)


Dielectric 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.



Circuit 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

Power 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.

Relays 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).


Slow Battery Discharge.  See the "Starting" section for more information.


Multiple 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.


Cruise 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.


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