Another cruise control/high idle issue.

Ive been chasing this for a week. Cruise/high idle would work, then wouldn't. Engine brake always works. I have read, diagnosed, read more and found nothing that could cause this.

Finally just 10min ago I fired the truck up to get some heat in the cab, and I try my high idle. It works. Since its dark, I flipped my marker lights on and the high idle kicked off. Marker lights off, it works again. Flip on headlights, high idle kicks off. So I have successfully figured out the issue, now I need figure out WHY its doing this. How would the lights equate to interrupting the cc/high idle function?

Truck is an 02 379 with a C15, btw.

 

Man, youre like my Dalai Llama

Noticed last night that when I step on the brakes, the side marker lights that someone installed, turn off. Let off the brake, they come back on.

 

I completely forgot to update this. I figured out that my high idle will work when all my lights are off. If I flip on my marker lights or my headlight, it disables my high idle/cruise. I believe the issue is related to some lights that have been mounted under the sleeper. I noticed that they blink opposite of my turn signals and actually go off when I step on the brakes. I still need to trace the wires and see how they're wired in.