Hello all, one of the main issues with my car (87’ 740)is electrical components not working. Such as the AC, window wipers and the horn. While it could be individual wiring problems I’m fairly certain it’s the fuse box and relay part.
One of the fuse ports had melted out and the previous owner had replaced it with a makeshift version. I have a replacement fuse box and relay area but have go no clue how to undo it without having to cut all the wires and reconnect them. Is that the only solution?? And should I just take it to a professional?
Thanks for the help everyone.
Fuse Box replacement? Help needed
Reubo I have a replacement fuse box and relay area
From what year model? There are subtle differences in the fuse / relay allocation and wiring between different 740/940 year models. (I found this out the hard way....)
If your replacement electrical centre is also from a YM 87, you shouldn't have too many dramas; if it's from a different year model, you may.
The absolute last thing you want to do is cut wires. On the underside of the electrical centre, the wires connect to the fuse points via Utilux-type blade connectors. There also should be a wiring colour code paper label affixed to the underside of the fuse box, and that's held in place by the wires fitting over the blade connectors. It should look something like this:
(This label's from a YM 89, so it is probably different to yours.... but you get the idea).
Your replacement electrical centre (fusebox) should ideally have the same label as the one in your car,
As you can (hopefully) see, the different colour codes on the label correspond to the different wires which need to be disconnected and moved from the old electrical centre to the new one. It's a very long and tedious process, and my guess is most auto sparkies will either charge like wounded bulls on angel dust to do this, or run away from the job like they are on it.
So you may need to tackle this yourself, and have somebody close by to give you a hand if needed.
If you're colourblind, don't even consider doing this job - bribe someone who isn't with offers of $BEVERAGE to do it, after the job is completed of course. Mixing up the colour coded wires will cause no end of problems, and that's easy enough to do even by someone who isn't colourblind.
The differences between year models and their fuse boxes include, but are not limited to -
Fuse #1 on year model X may have a different purpose(s) to fuse #1 on year model Y (and so on).
The power rails are wired differently on some fuse boxes. So the 'always on 12V' rail might supply different fuses with power between models. You need to be careful with this as, for example, the ignition system needs to be powered when the starter is engaged - and not cut off like many other systems on the 'ignition on' power rail.
You'll likely find that the fuse which juices up the heater fan motor is cooked, or about to cook (Different year models have different fuse numbers for the heater fan). The only real fix for that is to wire in a very heavy duty and high quality replacement fuse holder, which will take a fuse of the same Amperage as the original. The heater fan draws something stupid like about 15 or 20A, and the dicky little OE fuse holder contacts can't handle that many herbs, so they cook. I've had to replace the heater fan fuse fitting and modify the electrical centre in my 780 for that reason. It wasn't a fun job.
I wish you good luck on your journey, which is not for the feint of heart.
jamesinc added the Troubleshooting tag .
Major Ledfoot thanks so much! I have a 1987 740 Turbo. As far as I can tell the replacement fuse box is the same but is there a sure fire way to tell? And do you have any tips or tricks/which tools are handy for disconnecting and reconnecting the wires?
Cheers
And one other thing sorry! There is the one port and one relay which the previous owners did a patch/rewire of, is it fine to just connect those to the new fuse box panel?
The labels on the underside ought to be the same.
ObTip - you don't have to replace the whole relay tray, you can un-clip the fuse box component from the cradle and replace it with your new one, as long as they're from the same year model. (Tried swapping a 94 940 fuse box into my 88 780's electrical centre - it didn't fit because there were differences in the plastic mouldings).
Only other tip for doing the big wire replacement swapout thing I can think of is ... use good quality needle-nosed pliers and take your time.
Okay, for your PS which popped up as I was banging this in - what is that extra relay for? And as for that fuse on the lead with two blue wires - what number fuse is it replacing in the OE fuse box?
Major Ledfoot
So it’s not an extra relay but for some reason they’ve redone the K relay, which I believe is linked to the AC, hence my suspicions. And the fuse is number 16 which I also think is the AC. So my guess is something went wrong with the fuse and relay and they rewired both.
My worry is that the fuse will melt again on the new fuse box if I reconnect them. I also have heard that redone K relay making a slight buzzing noise before. I’m wondering if it’s worth getting the sections which were rewired done again in case they were dodgy and then doing the rest of the fuse box? I was thinking of doing the relays as well because that K has been taken out of the original.
- Edited
Check out the TP-31058/1 Green Book - I've just emailed a copy to @jamesinc for adding to the Oz Volvo Technical Library, so hopefully he'll have a chance to add it there soonish.
According to it, Relay K is the headlight relay. (pdf page 7)
Refer to pdf page 3:
Fuse #16 is the heater fan fuse for auto-climate controlled cars. Sooooo... ayup; it's cooked in the past (not uncommon).
Fuses #14, 15, 16 (plus #23) are power fed from the X15 terminal of the ignition switch. So if you're having dramas with the horn (fuse #15) it appears there's a problem with that feed rail on the fuse box.
Fuse #6 (which also seems to have gotten hawt 'n' heavy in the past) looks like it was the seat heater power feed.
Relays should not buzz, so some high weirdness is going on there.
Anyway, it might be an idea to check out that PDF first and see if it answers many of your questions.
Edited to add: Thanks James - you can look up the PDF now - it's there as TP31058_1 1987 740 760 Wiring Diagrams.pdf
Major Ledfoot
Okay, once again, thankyou. I think I’ll get an auto electrician to redo the wiring done by the previous owners just so I know it’s done properly and then I’ll try connecting the wires to the new fuse box.
However it does appear that I have an issue with that feed rail because 14,15 and 16 are the things I seem to have not working. What can be done about the feed rail? Because I haven’t got a clue what that is, cheers.
Reubo What can be done about the feed rail? Because I haven’t got a clue what that is, cheers.
It's represented here by the big green lines (& green arrow).
It's the power supply feed (or rail) from the ignition switch that supplies +12v from the ignition switch in X (accessories) and 15r (Terminal 15 which is ignition on; 'r' meaning engine running - as opposed to 15s, meaning ignition on, engine start) to fuses #14, 15, and 16 - with a link going off to fuse #23.
If you were to pull the fuse holder / box apart, it's literally a small metal rail at that point.
If you're not getting juice at 14/15/16, but there's +12v at terminal 30 at the ignition switch when it's on, there are only basically 3 causes -
- faulty ignition switch
- faulty connection &/or wire from ignition switch to fusebox
- faulty / broken rail in fuse box.
Okay thanks for that diagnosis, I’ll test if they are getting power or not and try and see what the problem is.
One thing I’m not sure if it’s important, is my ignition coil has busted at some point and leaked a thick black liquid, is there anyway this would effect these electronics? Or is it just a seperate issue? (I know it needs replacing just haven’t done it yet).
@Major Ledfoot I just dropped a new feature - you can now link files more easily (you'll see a new link to the right of each doc in the archive).
Reubo my ignition coil has busted at some point and leaked a thick black liquid, is there anyway this would effect these electronics? Or is it just a seperate issue?
Yes, it is.
The black liquid is a coolant for the coil windings, which get hot when they're at work. As you know, it needs replacing.
Major Ledfoot
Would it affect the fuse issues or no?
^ That's a 'how long is a piece of string' type of question. It COULD have an impact on the power / fusebox issues, if the coil has gone short circuit in some way due to overheating. Coil overheating could lead to an internal short circuit in the coil,, which would in turn lead to excessive current draw on that circuit and heat things up in the fuse box and wiring. (That said, I've written the above without examining the ignition circuit in detail).
Major Ledfoot ok thanks.
Well I have just done some testing with the multi meter while in accessories and I’m quite perplexed.
Fuses 1-10 all showed 12.85v when tested.
Fuse 11- showed zero although it had no fuse originally I just put one in to test it.
Fuses 12&13 showed 12.85
Fuses 14&15 showed -0.10
Fuse 16 (repaired fuse) showed 12.85
Fuses 17-22 showed 0
I tested fuse 23 by putting one of the other fuses in its slot but upon doing so it’s sparked with electricity so I quickly took it out.
I understand you can’t answer everything, but any idea what all that means??
Reubo Fuses 14&15 showed -0.10
Fuse 16 (repaired fuse) showed 12.85
Well, that's a problem. #14, 15, and 16 should all have juice.
Look at page 3 of the pdf (i.e. page 1 of the Green Book) and there's a table there saying which fuse does what.
Whoever did the fuse 'repair' did a bodgy, since 14 and 15 are supposed to have +12V from the same source as #16.
See the green line in the pic I posted before.
- Edited
Major Ledfoot
Hmm so maybe when repairing number 16 they have done something to ruin 14 and 15?
Any idea about 17-22 not showing anything?
- Edited
Reubo Any idea about 17-22 not showing anything?
Major Ledfoot Look at page 3 of the pdf (i.e. page 1 of the Green Book) and there's a table there saying which fuse does what.
Edited to add: You likely won't see voltages on those other fuses until the system / circuit associated with that fuse is switched on - e.g. you won't see juice on the headlight fuse until you switch on the headlights. So you have to know which fuse works for what component, and p3 of the Green Book tells all.
Major Ledfoot ah ok that makes sense.
I was wondering, do you think it would be worth swapping the fuses over to the replacement box and see if that help/resolves some issues?