No tail lights or brake lights

[Don Quixote]

It actually doesn't sound like a brake switch but rather what is supplying power to it. With our trucks, the brake lights and the parking lights were powered by the same source.

I had seperated the circuits and powered the brake lights from a seperate fused battery circuit. I did this to prevent the brake lights from ever shorting the other lights but also to avoid overloading the circuit while pulling my trailer.

If the brake lights only work with the headlights on, then the switch would only be getting power from a wire running after the headlight switch but before the headlights.