We have this odd problem where the brake lights on the truck work fine but when we have our 20-ton trailer hooked up the brake lights on the trailer come on with the ignition in the on position and stay on. They do not react to the brake pedal being pressed. Is there a separate switch for the trailer brake park lamps or no? Everything else on the trailer works but this weird problem with the brake lights. We know it's not the trailer as it works fine on our other trucks. Does anyone have any idea what this could be?
Take a test light or multi meter to you brake light connector on the truck and see what you have for voltage.
Auxiliary power-check the seven pin male plug.