Chevrolet Repair: Chevy Suburban issues, brake light switch, gas gauge

Question
First, problem we do not have any brake lights, I swapped the circuit panels in the back and I have also swapped the brake light switch. Next our control for the fan for ac and heat is backwards, high is off and off is high. The gas gauge is really shaky too. Any help would be great.

Thanks,
Joe

Answer
Hi Joe,

No brake lights?  Do you have blinkers?  Do the hazard lights blink in the back?  If you have these lights, but no brake lights, and the brake light switch has been changed, then I have to meantion that a circuit pathway goes through the headlight switch.  Possible this is bad.  If no blinkers, or brake lights, look for a bad ground.

Do all of your fan speeds work, only in reverse of it's setting?  Did this happen suddenly?  Did you just buy this truck?  What year is it?  Do you have the little digital screen system, or knobs on the dash.  This could be as simple as the plug is backward, or major as the cooling system brain is haywire.  Hard to tell without being able to see it.  

What do you mean the gas gauge is really shaky?  Does this mean that the needle jiggles back and forth quickly?  Or that it drifts?  Or that it is wrong alot?  Drift or wrong is indicator of bad sending unit.  Quick movement is electromagnetic interference.  This is caused by a stray signal going past the gas guage in the dash area.

Good Luck.

C J S