prodigy P2 brake controller acting funny

Maybe disconnect the harness from the P2. Put a meter on those harness pins as you apply brakes to see which wire is sending juice with the brakes. And also check if headlights on is sending any voltage to any pin on the P2 connector, it shouldn't, of course. On mine, it came with a generic connector going to bare wires, which can be wired in if the factory one doesn't make sense. Power, ground, brake switch can be easily found, and the trailer brake wire can be traced, and attached to the bare wire connector if all else fails. Got to have those brakes! I remember seeing more than one way to connect the 7 pin connectors, also, check that.