Hi Guys!
So this post is an extension of an older one (erratic cold idle). I have finally been able to conclusively determine that the reason why my truck is idling so erratically is that there is a short between the engine coolant temp. sensor and brake circuits (not sure which brake circuit, just know it has to be one that gets powered when you hit the brakes). Does anyone have any good advice on finding this short. I have a service manual with a wiring diagram already. Just wondering if there is any way to locate it without having to try to trace the wires up over around and through everything the engine bay.

 

You wouldn't happen to have a trailer light adapter installed would you?

Have you tested the brake switch yet? Do you have cruise control?

 

I do have a trailer light adapter and cruise control. Brake switch? Would that be the one operated by the pedal to turn the lights on?

 

The trailer light adapter could be shorting out and causing yer electrical gremlins. Try removing the adapter and see if the problem still exists. Those adapters are a known electrical gremlin creator...when they go bad.

Those vehicles with cruise control vs those that don't have a different brake light switch. You must make sure you replace it (if it's bad) with the same type. A non-cruise control brake switch won't work...