[klawockvet]

If I were doing it on a Model A for a trailer with no brakes I would get a 4 wire kit from local auto parts. The kit will have a flat 4 prong plug. Three wires will be insulated and one will be open. Make sure the car side has the ground hooked to the open/uninsulated prong. Hook a tail light wire on the car to the brown wire. If you dont have turn indicators hook the brake light up to the yellow wire and green wire. Hook the white wire to a good ground using a star washer. Use a star washer on both the car and trailer side of the white ground wire. If you have turn indicators on the car you will hook the yellow wire to the left turn and the green wire to the right turn. Same thing on the trailer and you will have a system that can hook onto most trailers. All the wires for the trailer hook up can be done at the rear of the car unless you add trailer brakes. If I were going to add trailer brakes I would use a 6 way plug. If I wanted to have a plug that was permanently bolted into the body or an adapter I would use a Cole Hersey 4 way plug and would use the same color wires. There are some who will argue over the color of the ground as it is proper to use black, not white for ground on a DC application. As a side note for those who think a Model A cant haul a trailer: My best friend in high school built a single axle horse trailer and pulled it behind his model A all over southern California back in the mid fifties.