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Questions and Answers

Strange Chevy S-10 Heater Problem

Q. Vincent, I'm having a strange problem with my truck that you might have an idea. 1995 Chevy S-10. 4 cylinder 5 speed manual transmission, 105,000 miles and runs great. For some reason when you switch the HVAC control from "OFF" to anything, heater, vent A/C, the brake light (idiot light) on the dash comes on and the speedometer drops to 0.

Strange Chevy S-10 Heater Problem

It started about two weeks ago and at first it was a momentary thing. I could have the heat on and be driving down the road and the brake light would pop on the speed would drop to 0 then everything would go back to normal. This doesn't effect the running of the truck at all.

Yesterday, 1/1/04, the problem gets worse and the light stays on, the speedometer reads 0 unless the HVAC selector is set to "OFF". The fan no longer works now either. I replaced the control panel (from a junk yard) today and still have the same problem.

On the selector there's a vacuum line connector and one plug with three wires, one green and two brown, two have grounds on them. If I pull this plug off the brake light doesn't come off and I can hear vacuum moving things when I change the selector but the fan doesn't work. Any ideas?


A. You may have a bad ground to the dash cluster. Check drivers side lower mount bolt above the parking brake pedal to see if it fell out. Some of these dashboards are grounded there with a big black wire and a star washer on a bolt. Also check the wires to the blower motor itself and make sure nothing is melted together in that area under the hood.

If you find nothing, try running a ground wire from the negative battery cable to a good spot on the dash frame and see what happens. If still no help, you will need a schematic and trace each problem separately, they may or may not be related.

Additional Information provided courtesy of AllDATA

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