Have a 1980 442. Have had now 3 Cutlasses with the rally gauge package.
Have taken these apart before.
The copper overlay looks really really good. Went through all like I have before and watched a video on G body garage on how to check everything and did just that.
Here's the issues.
Sometimes tach works sometimes not.
When I turn the headlights on for sure the tach doesn't work.
Sometimes the gas gauge works sometimes not. Especially not when lights are on.
Instrument lights do work though and the blinker lights do blink.
Motor is rebuilt 350 rocket out of a 1970 Cutlass not the original motor.
The oil pressure sensor and temperature sensor look really good but don't work on the instrument panel.
Voltage gauge either.
Any suggestions or anyone had the some issues.
Thanks

 

The fact that turning on the headlights has an effect on the gauges suggests a ground issue. You might try bending the terminals to apply a little more pressure on the copper trace. Is there a ground wire from the engine block to the firewall? Make sure it’s clean any tight.