Rear fog lights

Post Mon Jul 16, 2012 8:57 am

I'm after a bit of help! Having just repaired some rust on the floor and the bulkhead Ive finally got my car back together, now i checked all the electrics before putting the carpets back to save myself this problem but it seems I forgot to check the fog lights and they dont work.

Ive got power at the fuse (17 I believe) but nothing at the switch. I traced the black and yellow wire, which i think is the positive and it runs from the switch into a white multi plug and then seems to run down towards the rear. Not through the bulkhead like i was expecting.

if someone could give me a better idea of where to start looking for a problem id be very greatful!

Post Mon Jul 16, 2012 9:31 am

Two initial questions: Fog lights at which end or both? What car?

Post Mon Jul 16, 2012 10:06 am

Rear ones on my m3

Post Mon Jul 16, 2012 8:49 pm

Fog light wiring varies in E30s, depending on what market the car was made for.
All the on line wiring diagrams I've seen are for US spec. cars, which have very different foglight wiring from UK cars. The circuit diagram I have has been laboriously traced from scrap UK, facelift, RH drive wiring looms, so I can't say for certain that they apply exactly to a LH drive M3, which has largely pre facelift wiring.

Does the warning light on the instruments light up?
Do you have two black relays, K4 and K8 in the fusebox? (Not to be confused with the wiper control module.)
If the warning light doesn't illuminate, pull out the foglight switch, unplug it, then connect apiece of wire between pin 2 (yellow/black) and pin 4 (grey/purple).
Turn on the ignition and the headlamps.
The warning light and the rear fogs should light.

Post Tue Jul 17, 2012 8:18 am

Thanks Brian, I'm not sure if you aware of a chap called gustave but he has done a full diagram of a euro m3 but it just doesn't help me. I'm fairly good with electrics (although I hate it) but i cant read a diagram, I just need to know what wire would go where.

The problem seems to be with the positive, if I put power to the yellow and black and turn the switch on then the dash lights up and so do the fogs. It just seems very strange that I have no power and no blown fuses.
Since my last post I have discovered that the rear fogs are powered by fuse 15 with a jumper cable inside the fuse box to no 13 which seems odd to me. When I get to my car today I will check these for power.

I really don't think it's a break in the wire as I stripped all the tape form the loom, cleaned and checked for dodgy wiring and replaced with new tape while the interior was out.
Perhaps something has come loose in the fuse box as I had it pulled out the way while I was welding?

I hate to have to do this but I'm thinking the easy solution would be to take a switch live from the ignition put an inline fuse in and straight to the switch?? Or could I attach it to the front fogs and increase the fuse?

Post Tue Jul 17, 2012 9:39 am

Brianmoooore wrote: Do you have two black relays, K4 and K8 in the fusebox? (Not to be confused with the wiper control module.)

Post Wed Jul 18, 2012 8:05 am

Yes I've got both. Strange thing is they started working again, so I'm thinking perhaps a sticky relay is to blame.

Post Wed Jul 18, 2012 9:13 am

The flaw in that theory is that the power feed is by one relay when the headlamps are on and by the other when the front fogs are on, so they would both have to be faulty to give no rear fogs.
Faults that 'go away' on their own have a nasty habit of returning at inconvenient times - such as the middle of a MOT test.
Probably worth stripping down the switch and cleaning it.

Post Wed Jul 18, 2012 12:56 pm

Very strange, I do hate not finding a problem! They are still working but i might just buy a new switch anyway.

Post Wed Jul 18, 2012 7:24 pm

A quick clean up of its workings is all it needs. Very easy to do.

Post Fri Jan 09, 2015 2:42 pm

My rear fogs don't work, but I have both relays mentioned by Brian, and bridging the pins suggested brings the rear fogs on. What next?

Edit: I take the switch apart and clean it

Post Fri Jan 09, 2015 5:07 pm

beemerbird wrote:What next?
Edit: I take the switch apart and clean it

Correct!

Ben

Post Fri Jan 09, 2015 8:08 pm

Well I'm really struggling to split the switch open to give it a clean. Any tips?

Post Fri Jan 09, 2015 11:21 pm

A couple of small screw drivers, one down each side at the back. Watch out for the boingfuckits.

Ben

Post Sat Jan 10, 2015 12:34 am

Keep the buttons facing upwards when you pull it apart.

Post Sat Jan 10, 2015 10:54 am

BenHar wrote:A couple of small screw drivers, one down each side at the back. Watch out for the boingfuckits.

Ben

Worked a treat. Thanks for the warning re the boingfuckits.