The best place to start with these units is power and ground. If power and ground are in question, it would be in the best interest of the person performing the troubleshooting to run the pink wire directly to the battery (+) and the black and gray wires directly to the battery (-). Make sure that the motor has direct connection (heavy gauge wire like a 0 or 00) to the battery (-) terminal as well. You can go as far as checking for continuity from the pink wire that is connected to 12v source to the pink wire on each connector to ensure that there ate no breaks in the conductor.