85 GMC C2500 Dash Lights Not Working Please Help

[RustyPile]

Originally Posted by NWSooner

Thanks for the replies, its something else though. I'll keep at it......

Wrong assumption... Do you know where that green wire gets its power??? It's from the headlight switch. Actually, it's internally part of the tail light contacts. There is only ONE power source for the switch.. If you have just one light (headlight or taillight) doesn't matter which one) when you pull the knob, you have power to the switch.. The rheostat is on a "branch" of the tail light circuit.. When the tail lights are ON, power is sent to the rheostat.. That voltage moves through the resistor and exits into the green wire.. If you have tail light voltage at the headlight switch, that means power is being sent to the rheostat.. NO power on the green while having power to the taillights means that rheostat is bad..

That's how the circuit works --- no two ways (or "it's something else") about it......