Mattys1979Vette

I have a weird issue with my temp gauge in my 79. The guage normally works fine, but when i turn on my headlights the gauge moves when i turn my dash lights up or down. So if i have my dash lights up all the way the guage moves all the way to the right and if they are turned all the way down the guage moves all the way to the left. Any Suggestions?

0Willcox Corvette

Sounds like a ground issue to me. The headlamp switch is back feeding voltage to the dash unit.

The temperature gauge is controlled by the following wires looking at the connector from the drivers side seat.

The top wire on the left side is the ground. This wire is also a shared ground on the seat belt warning lamp, and the bulb lamp right below the gauge.

The second wire down on the left (driver) side is the input ohms wire terminal. The ohms comes from the sending unit off the engine to this connector and it should never have power on it, only an ohm's reading.

The second wire from the top on the right hand side (passenger) is the power wire for the temp gauge as well as the lower fuel warning, gen, amp gauge, and oil pressure.

Hope this helps.

I would check for back feed voltage on the ground wire (top left) of the connector.

Willcox Inc.