I just recently bought my 1990 Volvo 740 Bas /GL Sedan, the Fuse that controls:Warning Light, Turn Signals, Air conditioning Relay, Powered Windows, and heated front seats. Its location is fuse # 9, I've burned through quite a few fuses and tey were the correct amperage (15). It will only blow if the car is running, if just the battery is on I can roll down the windows and turn my blinkers on to hearts content and the fuse will be ok its only as soon as I turn the car on it will blow. My dad is an electrician and he says he thinks the issue is caused by whatever part transfers power to the components from the battery to the alternator.
Any help and suggestions would be great Thanks.

 

um. 'whatever part transfers power' is a big fat wire

that out of the way... blowing fuses means too much current through the fuse, which almost always means a short downstream.

but, its probably a good idea to check your battery voltage, first when the car hasn't been run for a couple hours, the 'rest' voltage of a fully charged battery should be around 12.6V at normal ambient temperatures (it goes up when its hot and down when its cold). when you start the car you should see around 13.8V at the battery, that means the alternator and its regulator are working 100%. if you see MORE than like 14.1V, your regulator may be bad (this is a little module on the back of the alternator that also includes the brushes).

given that you have good voltages, I find it odd that in accessory everything works, but with engine on, it blows fuses. I don't have the greenbook wiring diagrams for a 1990 740, just for a 1991 740/940 but they shouldn't be that different (the 90 is significantly more different than the earlier 740s than the 91, I believe)... so the following is based on my reading of the 1991 740/940 wiring diagrams, greenbook TP31781/1

fuse 9 and 10 are connected to the ignition switch pin 15L and that in turn gets powered in I and II (accessory and run)

according to the greenbook, fuse 9 is Turn Signals, Seat Belt Warning lights and chime, Power Window and Heated Seat relay, Electric Cooling Fan relay, Manual Climate Control, and the relay for the Parking Shift Lock (the one that won't let you shift out of park unless the engine is on and your foot is on the brake).

Does the 1990 have an electric fan on the radiator? Fuse 9 doesn't power the fan itself, it powers the coil of the relay that enables the fan if a thermo-switch says the engine is getting hot. This relay is under the hood, looks to be on the right fender somewhere.

the heated seats and the power windows are powered via a relay in the main relay panel forward the fuses behind the ashtray (remove the cigar lighter pocket/tray for better access), you might try pulling this relay and seeing if the problem ceases, its the leftmost relay on the aft row (closest to the fuses). again, fuse 9 provides the coil power to the relay, which switches the actual power to the seats/windows etc

fuse 9 provides power to the coil of the P-shift lock relay, which is under the dash near the steering column (drawing is non-specific past that), this relay is drawn as having 4 wires, blue-green (from fuse 9), yellow or yellow-brown, brown-black, and pink.

fuse 9 provides power to the door chime, which is in the forward row (farthest from you) of the relay panel, just right of the big round can in the leftmost position (round can is the light bulb failure sensor). you might pull THIS relay and see what happens. fuse 9 also directly powers via blue-green wire to green-white wires the two seatbelt lights, one in the instrument panel and one by the rear seat ashtray. these lights are grounded through the chime/relay module just mentioned. if the wiring to the rear seat warning light got pinched somewhere, THAT could be causing this.

fuse 9 also goes to a blue-green wire that goes to the turn signal switch on the steering column, looks like this is used for the emergency flashers. that flasher/turnsignal circuit is kinda complicated (and very hard to read in my 1991 book, that page has a poor scan).


of these circuits, the last two seem most likely candidates for problems, but its really hard to say, without getting in there with the wiring diagram an a digital multimeter and troubleshooting. I didn't list a bunch of connectors in the middle of some of these circuits, but they could be unplugged to isolate some of the circuits to further aid in testing.

 

Ah, the new (to you) car blues. I just got a 1993 240 and have been beating my head against it from day one.

The first thing you need to do is get yourself all three manuals, Bentley, Haynes, and Chilton's (in that priority order) Even though Chilton's is generally crap, sometimes they have some information that the others don't or some diagram is easier to read and they are usually pretty cheap. None of my books have a circuit diagram for your car. You might be able to find something on the internet. I'll leave that to you.

Second, I wouldn't necessarily trust the label on the fuse panel. I have read of some of them listing things differently from how the car is actually wired. Even some diagrams will contradict each other. You gotta get all the clues you can and do some testing with an ohm-meter yourself sometimes. Usually, an old hand around the forums will eventually chime in with the good scoop.

Third, "whatever part transfers power to the components from the battery to the alternator" doesn't really make much sense. Power is transferred from the alternator directly to the battery by a big, fat, red wire. The one that connects directly to the post on the battery. The parts that transfer power from the battery to the components are called wires.

Fourth, If the car starts and runs normally with the fuse blown or out then you know it doesn't control anything really important, such as the ignition or fuel injection computers, or fuel pumps. So at least that much is good.

Fifth, things are usually wired in this order: Battery, Fuse, Switch, Component, Ground. But not always. Sometimes the switch and component are swapped. Rarely will anyone ever connect the battery to the component first because if the wire from the component shorts then it would burn out the component and the fuse wouldn't be able to help. But then you never know who may have been messing with what on cars this old.

Sixth, as a former electronics technician, my advise is to:

1. Get yourself a halfway decent volt-ohm-meter.
2. Pull out the fuse and make sure that none of those things work with the fuse out. This will let you know how accurate the fuse panel label is.
3. Disconnect (not just switch off) all those things things you listed and risk one more fuse to see if it still blows. If so, that means there is something else shorted that is only turned on while the car is running but isn't necessary for the car to run. We can brainstorm about that later.
4. Figure out which side of the fuse goes to the components. There are a few ways to do that:
   1. Look closely behind all the fuse connectors, down each side. Sometimes you will be able to see that multiple fuses are connected together by a wire or strip of metal. That would be the side that gets the power. The other side is the one that goes to the components.
   2. With the ignition on but not running and the fuse out: Check for 12 volts on one side of the fuse connector or the other. The side without the 12 volts goes to the components.
   3. Your model of Volvo may have some standard for which side gets power and someone here may know it, or they may know which side gets power for that particular fuse. I have no clue.
5. Once you have figured out which side of the fuse gets power (the "hot" side) and which goes to the components: With the fuse out and the car running (and all those other components still disconnected) connect your ohm-meter between the side that goes to the components and ground. (Be careful NOT to touch your ohm-meter to the hot side or you will burn out your ohm-meter as quickly as that fuse!) I'm guessing you will read close to zero ohms. That means you have a short but the short is likely AFTER some relay (meaning between the relay and ground) that is only being turned on when the car is running.
6. Turn the car back off. Does the ohm-meter now read infinity?
7. Start to turn the car back on but don't turn the key quite far enough to actually start the car. Does the meter drop to zero again?
8. Start the car and then turn it off again. Watch for the exact moment the meter switches from zero to infinity. Is it as soon as you turn the key? Or only after the car actually stops running? That could give us a clue.

One final note: It is possible that some idiot rigged something else in to that circuit that is just too much for that fuse. Look around to see if there are any extra electrical accessories and disconnect them too. If the meter stops dropping to zero after you disconnect that thing, then you have found your culprit.

 

Wow, Yes! Thank You Pierce. I will have to evaluate and meditate on this load of information you've dumped on me. I greatly appreciate it. We are going to take a closer look at the relay board and do some troubleshooting based off of what you told us. Thanks

 

Thanks Grant to you as well didn't realize somenone else jumped in. So far I've noticed the diagram in my manual and the sticker on the back of the ashtray have been accurate. I have the Chilton book coming in the mail next week, I'll probably grab those other two like you said eventually. Yes I'm thinking the problem is minor, I can still drive around if I need to, its just really hot in Texas, and that one fuse controls both AC and windows, and not having turn signals kind of sucks too. But the guy who had it before me apparently always serviced it well which is good so I'm hoping this the only issue I'll have with it for a while. First car too, worked perfect at the little dealership I got it from go figure.

 

there is no bentley book for 740's, sigh.

the haynes and chilton books are good for wiping something, or starting campfires.

you want the greenbooks. they used to cost $59 each or something as printed books, now you can buy them on DVD from VCOA or various vendors.. there's a DVD for each family of cars, 240/260, 740/760, 940/960, etc. they have not only the wiring greenbooks which have the accurate schematics (if you follow the supplements), but they also have the mechanical books, with the dealer procedures for all sorts of major service operations, like overhauling the differential. many of the greenbooks are generic, for all 7/9's, but the wiring diagrams are for every year. there's a a couple books on fuel injection theory and practice.

 

I also should add... a 1990 740 is closer to a 940 than it is to an earlier 740.

 

Hey Pierce, one more question if you feel like answering. Regarding what Grant said about someone installing something or messing with the original wiring, I found a little toggle switch located close to the hood release, I have no clue why its there or what it does my dad said someone could have jacked up the wiring trying to install it, he said it doesn't seem like it was originally there. Just wondering if your volvo (assuming you own a 92')has something similar or if someone definitely put it there. Can't find it in my manual but its not always descriptive about these things.It just says on or off around it, we flicked it a bunch of times to see what it did, but we didn't notice anything. If you've got any clue let me know. Thanks

 

nope, nothing like that on any stock volvo I've seen.

pop off the driver kick panel, and the knee brace (requires a torx driver of I forget what size) and you should be able see the wiring, and where it goes, what color wires its connected to would let me try and guess at least what its doing.

I've seen switches like that do a range of things, from powering aftermarket accessories to fuel pump kill switches to homebrew burglar alarms.

 

Good lord so many wires I took off the panel the two wires coming from the mysterious toggle switch are black and grey I can see black gets grounded to some metal plate, grey goes up and is seen taped together with: a light brown wire (it branches off to another bundle of wires), a turqoise wire (goes along the bottom of the door frame), and another black one grounded the same as the other one mentioned before. Don't knowif that helps.

I'm also trying to get the cigarette lighter/ tray thing to come out so I can get a better look at the board with all of the fuses, there's just one screw its hanging on by, on the inside-impossible to reach .

I left out some crucial details though. It not only happens to fuse #9, it also does it with 16. I just forgot. They both have something to do with A/C function. And like I said, when just the battery is on everything works perfectly, when I turn the car on it'll take maybe 4-10 seconds before the fuses will blow. If that tells you anything. Thanks

 

wait, if both sides of the switch are wired to ground, then that switch does NOTHING. huh. unless maybe there's a resistor or something buried in the taped junction.

I'm assuming your ground is the metal plate on the inside of the fender near the drivers door hinge? thats the ground used for the speedometer and cruise control, there's one on the passenger side thats used for all the rest of the instruments and fuel injection computer, etc etc.

is this a sedan or wagon? can you see that turquoise wire anywhere in the back of the car ?

the rear fog lights on a 91 (I don't have wiring diagrams for a 90) are grey. the rear door courtesy/safety lights are green w/ red stripe (I'll write this as green-red).

the left turn signal is green.
the power antenna has green-red, green-grey wires to it.
the left rear door speaker has a yellow-brown and a yellow-grey (which mutate to yellow-white and white at the speaker)

the rear window defroster has a yellow wire.

the left rear door power window wiring is pink, green, and grey up there (changes at a connector at the B post)


(all the above wires route down the driver side door sill)


oh, re the cigar lighter. it has a plastic bezel that just goes around the lighter socket, this unsnaps and comes off, to expose the screw or two thats holding it on.

 

Alright! Thans for the tip on the cigar lighter.
I have the sedan.

I'll try to explain it better, the grey wire is the lead from the toggle it originates from underneath the steering wheel, taped together with the other ones I mentioned. The second wire coming from toggle (black) is grounded to the metal plate. The other black one I was talking about I don't think has anything to do with it, it was just one of the wires taped with the grey one, its apparently a ground for something else.

My dad disconnected the power antenna from the trunk. Some yoohoo apparently bent the antenna up a while back so it can't withdraw back down.

 

oh, so that tape spot isn't a splice, just where wires are bundled together? hmm, that makes it tougher to guess where it goes.

 

Yeah tell me about it, its hard to tell where anything goes, its such a huge cluster of wires under the wheel. I found this page.
WIRING DIAGRAMS - Welcome to Ohio University

to show my dad when he gets off, he's got all the tools with him. I was just wondering though would it be bad idea to disconnect the toggle, would that change anything?

 

phew, those are much harder to read than the 'greenbook' official schematics from Volvo. however, I don't have a 1990, just 1991+.

I think before disconnecting it, I'd see if the grey wire is hot (+V) when the switchis 'off', with or without the ignition being turned on.

this grey wire, does it look like the other factory wires? hard thin insulation, same diameter as most of them? plain grey is fairly uncommon, only ones I've found o my 91 diagrams is some of the speaker wires (insane to ground that), and the seat belt rear warning light (also insane to ground that). there's a grey wire involved in the rear left door power window, but I doubt that would be it (and grounding that would blow fuse 8 when you operated the left-rear window, too)

 

Well it looks like the other wires in size, fuse 8 is ok, I checked. Its funny you mentioned the driver-side rear window is the only window that doesn't work/ hasn't wporked since I got it.

 

BTW< the antenna masts are inexpensive and easily replaced. But if you never listen to the radio, then don't bother.

 

Thats good to know.

Hey Pierce just wanted to say thanks for all of your help. I got my brother involved autonerd. He pulled back the ac control and found a wire that was melting everything around it, which explains fuse 9 and 16's relation. The toggle wasn't the problem, we'll just worry about it later.

Thanks again.