I just purchased a 1956 aljo and it has three black wires for the trailer hookup that aren’t connected. I have two black wires coming from the left side and one coming from the right? Does anyone know what they could be. I was thinking maybe grounds but not sure.
Most trailers have at least 4 wires; Ground, Left Turn, Right Turn and Running Lights (Tail Lights and Markers). Trailers with brakes have two more wires originating at the brake hubs. Brake wiring is usually heavier than regular tow wiring. Look at the backside of your wheels for the two brake wires.
My 56 Aljo had brakes but parts were no longer available. (huge round plates with a small magnet) Depending on the weight of your trailer, you may or may not need brakes by law. They are always good to have. In your case, I'm thinking a new axle and brakes may be necessary.
It sounds to me that re-wiring your trailer would be the easy way to go. The Ground is straight forward-drill a quarter inch hole in the frame and bolt the ground wire to the frame. A crimped "ring terminal" keeps it neat. The ground is all important in a 12 volt system, so be sure the connection to the frame is clean and tight. The RV universal color code for todays wiring dictates that the Ground be white.
There are only 3 wires left to complete your tow wiring. I always recommend following the RV 7 way color code. RT will be BROWN, LT will be RED and Running Lights will be GREEN. Most of us run a white ground to each light fixture when the trailer is down for repairs. In the old days, manufacturers relied on the skin for lighting grounds, but this method isn't reliable.
Please peruse our stickie threads in this section for more info on testing and 7 way vs. 4 way wiring. Further questions welcome.