I have a 1995 XJS Conv 6 cyl. With the car running, If I turn the dimmer the tach will change. If I turn on the signals, the tach will pulse in time with the signal.
I suspect it may be a ground. Any thoughts? Thanks, Mike
Located outside Phila. Pa

 

I think you are right about the ground.

 

Any suggestion on where to look first? Thanks, Mike

 

R
I would suggest: Remove the cluster, clean up the earth bar contacts (the earth bar runs along the top of the cluster and several bit of the flexible circuit board are earthed to it. Clean carefully all the circuit board to instrument contacts where they attach. Add an extra direct earth from the earth bar to the car frame.