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