M920 Solenoid by Ether Can Under Hood Melted - Headlights Out

[Construction]

All of the sudden when I cut the headlights on, the truck shuts down. It seemed like a short circuit, the volt meter pegs to zero (all the way left). I have spent hours and hours trying to trace the issue.

I discovered that my solenoid has melted (the one by the ether can on the drivers side) and I am trying to trace why. I have the 12 volt hot lead traced and it is fine. The other red wire (8 gauge) goes under the fire wall on top of the transmission and I am hoping one of you guys knows where it goes.

That wire now reads like it is straight to ground. If I run a 18 gauge wire across the lugs on the solenoid (as if to connect like the solenoid would) - the wire gets super hot and will melt the sheathing.

Truck runs fine with the lights off. Blinkers and brake lights are fine.

 

[commandojeff]

Use the manual to try testing the Protective Control Box. Does the truck start fine? My friend just picked his truck up and it was doing the same thing. Swapped the box out and everything works fine now.

EDIT: I didn't realize this was for an M920 until now... Not sure if my previous statement will help you much as that truck was an M939 series. Good luck!

 

[Construction]

OK, found shorted wiring for the headlights. Fixed.

The solenoid beside the ether can seems to feed into the transmission, guessing for the heaters/defrosters. This took all day - so that is all I have for now. Anyone who has worked on these CAT transmissions would know.

Help???!!!

 

[vinceM920]

I,ve had the same recurring problem with my headlights killing the engine. I have looked forever and cant find a short. Where did you find the short on yours??

 

[Construction]

I found the "hot" wire in the light system that had worn through and was grounded.

It took a lot of time to find, found it at the rear passenger side.