77 Sovereign rear lites
The trailer lights work off of three wires. One wire for the running lights, one for the the left turn, and one for the right turn.
The brake lights work off of the the turn signal wires.
My 72 only had turns and brakes on one pair of lights.
Straighten up the wires in back, and check the junction box under the gaucho. This is where I found most of my problems in the 72.
Oh, if you don't have one, get a test light. You will need one!
The fact that I am opinionated does not presuppose that I am wrong......