Strange fog light issue after HID low beams installed

[hella 325]

Hey guys. I installed Depo projectors and DDM HID low beams in my 1993 e34 and the fog lights quit working. They were working fine before the install.

No light on the dash or anything when the switch is flipped.
I checked the switch, the bulbs, and even tried another LKM.
When the fog light bulbs are unplugged it gives me a bulb error on the dash and that goes away once bulbs are back in place. Which tells me the wires are not cut or shorted.
When the low beams are unplugged I do get a low beam error as well that goes away when they are plugged back in.
I unplugged all low/high beams and tried again, still no fogs with either LKM.


Anyone have a clue is happening?

[Jacobw]

Get your voltmeter and start testing. Make sure they're plugged all the way in. I've noticed they have to be plugged in pretty far for them to work. Make sure your running lights are on and try the fogs. Check the fuses, the relay, switch, lkm, and grounds. If you aren't getting any power to the light check the switch, no power to the switch check the fuse, if you aren't getting any power to the fuse check it's the lkm or a bad wire.
You said you checked the switch, is there power? When you switch it does it switch power? Check for 12v at yellow/violet and yellow/grey at the switch when it's switched on. Does it have a ground?
Highs and fogs have the same ground check those.
Check the CCM. Pull fuse number 6 and see if they work.
Check fuses 2,3,5,7,13,14.
Check pin 17,18 and 16,32 while switched on at lkm
Voltmeter and order of operation. Test to see if there is power AND ground everywhere.
If you understand wiring diagrams this will help
http://www.armchair.mb.ca/~dave/BMW/e34/e34_93.pdf

[hella 325]

I just downloaded that wiring diagram a little bit ago. All fuses are intact.

How do I check the ccm? is pulling fuse 6 to check that?

Is the high/fog ground up by the lights or back under the dash?

To my understanding there isn't a relay, except for the one inside the lkm. How does one test that one?

When you mention pins at the lkm, do this with the lkm unplugged?

Thanks for the help i'll try checking the things i overlooked tomorrow!

[Jacobw]

The LKM is the relay. LKM is basically one huge bunch of relays, but if one thing needs to be soldered in the lkm doesn't mean the lkm is toast. Check pin 17,18 (power in) and 16,32 (power out) on the LKM. I believe the fogs ground to the highs, so chase the harness from the fogs to the highs. pull fuse 6 to check ccm, but your blinkers will stop working so then replace the ccm.

[hella 325]

I tried a known working LKM and got the same exact results. I checked all solders and they all look solid.

I pulled fuse 6 with no difference.

K, I just did some probing, everything has a good ground. However I came across a strange reading.

The passenger fog light gets 9.5ish volts when the engine is running. 12v when headlights are on (doesnt matter where fog switch is)

The passenger side fog light gets a few mv no matter if lights or fogs are on. This is perplexing.

[Jacobw]

you test the switch?

[hella 325]

I have and it's behaving properly. The weird thing to me.... if the socket is getting 12v why isn't the light working? And why is one side getting 12v with the headlights and the other not getting voltage ever.

[Jacobw]

Bad wire somewhere. Only thing I can think of. Go stand in a puddle and start shaking wires while holding on to a bare metal part of the car
Toggle switch time?
I was tinkering with this idea doing an LKM delete and just running a toggle board as I have like 600 rocker toggle switches and a bucket full of relays and a bunch of spools of wire from building "racecars" aka dirt track 4 bangers and parking lot warriors

[hella 325]

I dunno, doing that would be admitting defeat... I'm determined. Have you replaced the highbeam/blinker stalk? Was talking to a buddy with a different car who has very similar issues after HID, and he replaced the stalk and everything came back to life.

[Jacobw]

Like the multifuction switch? Never replaced one in a bmw but in other cars it required taking the steering wheel off. There is probably a thread some
where on the forums about replacing the multifuction switch.

[demetk]

Do the high beams work. On low beam mode does the high beam indicator light up? You don't get fogs when the high beam circuit is active.

[hella 325]

Yes high beams and the indicator light up.


I just got them to work... I put Philips Crystal vision bulbs in the high beams (was planning on it when i swapped to the projectors but was just waiting on them. When I swapped the standard h1 to the philips I took a bit of sand paper to the ground pole on the light housing just to clean it up a bit. Apparently even though the grounds were showing good with a multi-meter it wasn't enough to get the fogs to want to turn on. B/c now they work fine.

[Jacobw]

There you go it was a ground! Congrats of finding it.

[student2018]

Similar problem on my E34. After replacing OEM high beam bulbs to LED bulbs, fogs stopped working, but when the fog switch is ON, high beams are on at ~5-10% of power. Checked everything including wiring, switches, etc. The problem was solved after I installed the old halogen bulbs back. Looks like the fogs require to have the circuit in high beams to work.

[Singing6]

This is all to do with how the LKM prevents US cars from turning the high beams on at the same time as the fogs (illegal in every us state afaik). I covered how to undo this in my lkm mod guide.


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