Originally Posted by catz66
Locate the orange wire at the back by the trailer connector. It should connect to the center terminal in the connector.
On mine, the center is the reverse light and trailer surge brake lockout pin. +12V is one blade of the ring, the one immediately clockwise of the index in the truck socket.
The OP should verify which one it is, unless of course there is only one that's not connected. But then, the trailer plug must match, too.