Instrument Cluster light problem, Chevy P/U

[radarrider]

91 Chevy, Silverado 1500, 350cid, Auto Trans, 149712mi

I have an Instrument Cluster light problem. When I turn on the Headlights I have no dash lights. The T/S lights in the cluster stay on but flash when T/S are on, The Temp and Oil gage on the left side go up, The Fuel and Batt gage on the right side go down, The electric Speedo works ok, but none of the dash lights work. The gages and T/S lights work normal when the Headlights are off.

I thought it might be a bad ground, but it is a sealed cluster. I cant get to the back of the plug to back probe it and donft have anything showing the wiring of the plug.

I also have an unrelated intermittent problem with the Radio and Heater control. The Heater / AC control head will go totally dead and the Radio wont change stations or seek / scan. It will only power on / off and have vol control. Then a week or so later the Radio and Heater / AC control work ok.

[idol]

Hi radar, for the description you gave......it sounds to me like your suffering from a worn light switch. The light switche or have are of a double pole type. Which means that when it is activated you can select if you want only parking lights (which includes the instrument lights) or headlamps and the parking lights/Instruments. In this type switch, when the second pole is selected and the lights on the cluster seem to either dim or go out completely, I always tend to start with testing the switch for pole failure.
The speedometer is a separate circuit and power source all its own, as well as the radio and heater.
Your radio and heater do (in some of the earlier vehicles) share the same power blocks. What you are describing sounds to me suspecsiouly like your truck has this type power block and if so.....it sounds like it is loosing from the components.
If you were to bring your vehicle to me for the symptoms you described, I would begin my troubleshooting process at the two locations I mentioned above.
Check these areas and come back to let us know what you find and we can then help further from there.................................IDOL