1999 Suburban fog lights, dash lights, tail lights won't shut off.

[ScottK]

On my 1999 Suburban K2500 6.5, the Fog lights, dash lights, and tail lights won't shut off.

 

I replaced the headlight switch but that did not help. I have to disconnect the batteries to shut them off. Taking out the fuse does not help.

 

Any ideas? Thanks.

[ScottK]

I sort of found the problem. It is somewhere back in the trailer wiring harness.

I was told in another forum that "Before GM started to use Body Control Modules, lights, and/or, their control circuits were switched on the ground side, instead of the hot side.
The reason for this was if there was a short, the lights would stay on, instead of blowing a fuse, so you could get home."

I found one connector that was not together properly and I could see that all the plugs were totally corroded. I poked it all out with a screw driver and one plug was complete corroded away. Once it was clean the lights went out. When I stick a screw driver in between the plug that is gone the lights come back on. There is so much corrosion back there that everything needs to be cut off and redone. Oh the joys of salted winter roads.