Electrical issues on cars are the absolute most maddening things to diagnose and fix. I’ve restored several cars and worked on every car I own and the one thing I loathe to do is figure out an electrical failure. Even in older cars, it’s a pain in the ass.

I have an 89 e30 and one time the dash cluster started acting up. Essentially the tach and speedo weren’t responding (they’re not cable driven). Took out the cluster, checked all the connections, checked the wiring diagram to see if there were any potential grounding points I might want to consider. Nothing.

Finally called a local bimmer indie shop and asked them what they thought and they directed me to the small reverse light switch wire that feeds down through the shifter hole into the transmission tunnel. Apparently it often rubs against the body and becomes shorted. I looked and sure enough it was bare. Patched it and all was well.

This wire, mind you, is not at all on the dash cluster circuit. There’s no reverse indicator light on the cluster or anything like that. I would have never had any reason to suspect it was the problem. This is the nature of automobile electrical issues.