no reverse lights

[bbig119]

I posted a while back about the dipping mechanism being flaky on my passenger mirror (http://www.bimmernut.com/forum/showthread.php?t=42361). Ross asked if my reverse lights were also non-functional, and it turns out they aren't working. I've spent some more time trying to figure out what's wrong and have some additional details. I'm hoping someone here might have some suggestions on where I should look to find this electrical gremlin.

I've got a 94 540 with has had an auto-6 speed manual swap. I should point out that the license plate warning, mirror dipping and reverse lights were all working fine up until a month or two ago when I did actually have a blown license plate bulb. The mirror problem started before got around to changing the bulb, and I did not notice the lack of reverse lights until Ross asked me to check so I do not know exactly when they stopped working.

Symptoms/details:

• No reverse lights(bulbs look fine)
• Reverse switch at transmission replaced without change.
• When car put in reverse the OBC and radio dim as if the headlights were on. The backlight on the OBC will pulse some.
• Also when the car is put in reverse, I get a license plate light warning on dash although these bulbs were recently replaced and appear to work properly. I believe there are other things that may trigger this warning, but definitely reverse is one.
• The passenger side mirror dipping mechanism is still flaky. It doesl dip when car is put in reverse, but will also sometimes dip when not in reverse. I think this has something to do with either throttle('acceleration') or bumps.

Based on this, I think that I may have a wire with a bad ground or possibly a short somewhere but I'm not sure where to start looking. Is it reasonable to assume that the problem is upstream of where the passenger mirror and reverse lights split since both are having problems?

I'm also not sure what the relation is between the license plate warning and the reverse lights.

Oh, I've scoured the Bentley and downloaded some wiring diagrams that I found from a link on Shoguns website and if the document is correct the reverse switch signal will split for the mirror and reverse lights somewhere in the back harness(x428) but there is also some module down near the peddle cluster(x251) that may be a suspect. That's what I've got and I'll take a look for these the next time I have a chance.

Here is a diagram from that pdf

[bbig119]

I've done some more forum searching and I've got a few places that I will look as starting points. I gather there is a wire harness in trunk lid for the lights and its not uncommon for one or more wires to break and short or intermittently work. This would explain the connection with the license plate light.

The second place to look it near the foot well on the driver side by the console there might be a connector of some sort where the reverse wire passes. I also need to check fuses. I looked over the list of fuses in the Bentley last night but couldn't find a fuse that involved reverse that could blow without me noticing other problems.

[tim eh?]

I had my reverse switch go rusty, but I can't offer much besides encouragement - looks to me you are looking at the right stuff.

I would try and find the reverse switch and see if you can bypass it to get your stuff working again. Then at least you know if your problem is on one side of the switch or the other.

[yaofeng]

The 540 auto's reverse light function is taken by the transmission through its electrical harness to the EGS computer. So when the PO did the conversion he'd have to add a two prong Bosch connector to connect to the reverse light switch on the 6 speed gear box. The splice would have been done at the shifter. That what I did.

You may want to check the seating of the Bosch plug (unlikely to come loose) on the driver side of the gear box and also remove the panel under the shifter inside the cabin to check the splice.

The picture shows what I did. He should have done something similar.



The descriptions were here.

http://www.bimmerboard.com/forums/posts/276021

This is the extent to which I can help.

[bbig119]

I fixed the problem here. I had one fully severed wire and three or four others with various amounts of exposed metal in the wire harness that runs to the trunk lid. The cloth wrap had worn away at the clip that next to the trunk hinge. Its actually a bastard of a clip and its easy to see how and why wires would wear away here.

After some tricky soldering, I wrapped the section in electrical tape and then in plastic tubing and used wire ties to mount in a way that that I hope will be less abrasive to the wire.

Definitely a pain the ass and a tricky spot to access-- hopefully the fix holds up for a while; at least the winter.

Thanks for help