I just finished doing a heater core replacement the other day on my '88 740t. The heater works great, but my car is now having some pretty significant electrical issues.

My car sometimes has trouble starting (as if the battery was dead), though it often just starts up fine. Nothing on my dash is working properly; the only dial that moves is the turbo dial, and the only lights that will come on are my turn signals, high-beam light, and overdrive light. My radio will turn itself on and off (sometimes rapidly).

A couple of special things to note are that the overdrive light comes on when I start up my car (always), even though I never push the overdrive button. Also, no lights show up at all on my dash until I turn my headlights on, at which time both of my blinker lights come on (and stay on, they don't flash) and my high-beam light comes on (even though the actual high-beams on the front of my car are not on). All of my car's external lights appear to be working fine.

I had hoped that it was just a problem with my battery, but my car is acting the same way with a brand new battery in it.

The only things that I think could be causing these problems are either the relays or my shifter. I really didn't touch anything else electrical while changing out my heater core (that I know of). I did take apart my shifter assembly in order to clean it out, but I think I put it back together properly. I checked the relays, and the only thing that I did that was able to change how my car was acting was removing relay 'K', which would cause everything on my dash to turn off.

Can someone please help me try to figure out what is causing my electrical problems?

 

did you have to remove any ground wires
that may not have been put back ?

 

I did not (knowingly) remove any ground wires. I did disconnect the battery before starting work on the car, though (and yes, I did reconnect it afterward).

 

i am guessing that you will have to take the dash apart again
you must have missed or accidentally disconnected something

 

I've gone through and unplugged things one by one, and nothing so far has made any difference.

I have also tried removing fuses one by one, and the only one that seems to have an affect is fuse 21. When I take it out, the two blinker lights and the high-beam indicated light turn off (and then work properly, i.e. the high-beam light will turn on if I switch on my high-beams).

 

double check the ground at the battery
and the ground from there to the frame
also the woven ground straps
found at the rear of the engine
to the frame.
electrical issues are hard enough to diagnose
without the disadvantage of being miles away.

 

I found and fixed the problem; there was one cable that came detached from the cluster. Don't ask me how 1 detached cable can cause a short with the battery and between multiple fuses. I'm just glad it's working.