2003 Chevy pickup. The brakes lights stay on and the cruise doesn't work when the headlights are on. Turn the headlights off and the brake lights go off and the cruise works. I'm thinking it may be the brake sensor (on the pedal), but the brake lights still stay on when the sensor is unplugged.
I'd appreciate any input, and if it is the sensor, how does it come off (can't see the back side of it)?

thanks for your help

my first thought would be the multifunction lever(on the left side of steering column). wonder if it's shorting inside the wiring harness.

I'm betting there is a short somewhere in the wiring harness.

The cruise not working is related to the brake lights, when you tap the brakes to kill the cruise under normall operating conditions, it also sends a signal to the ECM killing the cruise.

something similar happened to me. I took it to the dealer and they found that a tail lightbulb was melted, causing a short. So whenever I turned on the lights, the cruise would go off, and other strange electrical stuff. Stay away from cheap china-made light bulbs!

Does the 2003 have a brake light switch on the brake pedal? I have replaced several of those over the years.

you have a short somewhere,you are cross feeding voltage for it to be doing what it is doing,maybe in the multifunction lever,could be in the headlamp switch etc....

I know some of the older Chevy's had a button underneath the brake pedal that would stick when it go dirt in it. I would have to put my foot underneath the pedal and pull back on it to get the brake lights to go off. Might be worth checking.

thanks for all the input. I will look for a short when I get a chance. I think the brake switch on the pedal is working.