The Brake controller is Reese Brakeman. The black wire does send 12v
to the trailer via the trailer plug when turned on. Here's some info from their website, but I'm not sure what to test:
No Green LED with trailer connected.
The Envoy needs to have a complete circuit on the blue wire to the brake magnets then to ground to turn the Green LED on. Possible causes: •Trailer not connected properly or completely.
•No power on the Black wire of control.
•Poor or no ground on the White wire of the control.
•Open in the electric brake wire.
•Open in ground wire of brake circuit.
•Tow vehicle and trailer mis-wired.
•Power back feed on the Blue wire.