Perplexing Electrical Gremlin
 

I spent some time last night trying to diagnose the non-functional instrument lights in my tach. All of the other gauges light up as they should when the parking/headlights are on, except for the tach. I pulled the tach out of the dash to check the wires/bulbs, and they all are ok. I cleaned all of the connections.

Now here's the wierd part. The lights work if I touch the body of the tach to the bezel of the oil pressure gauge. This leads me to believe that there is a ground problem, but there is no facility for any of the other gauges to ground metal to metal either, as they are all held in place in the dash by a rubber ring. The brown ground wire coming off of the back of the tach is hooked up and has a clean connection. I traced that wire down to the grounding point, and it completes the circuit.

What am I missing? If there was no ground at all to the tach, I'd assume that the gauge itself would not work along with the lights. Any ideas!?!??

Thanks,

Brad
'83 SC Coupe

Have you used a multimeter to check the resistance of the ground wire end-to-end?

Regards,

Could the ground spade plug on the back of the tach not truly be grounding to the guage chassis?

You obviously have a grounding problem. Just take a piece of wire and run it from a good ground to the tach. Lights work? If so, rewire the ground.