Perplexing Electrical Gremlin

[BradH]

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

[Jim Richards]

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

Regards,

[cstreit]

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

[Rot 911]

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.