w107 grounding problem
 

gauges go crazy when turn signals are applied. have inst. cluster out but need wiring diagram or guidance to isolate which pin, etc. is ground. ..for example:.. each guage has a brass stud fixing it to cluster. assume this is not a live connector. guage also has brass rivets coming through circuit board. continuity check between these 2 is live. any ideas short of $380. for new guage cluster?

Going from memory here, but I believe there is a central ground on the firewall behind the instrument cluster. Believe there is another on the passenger front sidewall by the OVP relay. One more I think, but don't recall where.

Also, I have an instrument cluster I bought off eBay that I can part with reasonably if you must have one.