Re-Wiring Old 4-Wire Boat Trailer Plug With a New 7-Way Trailer Plug

Question:

My fathers boat trailer has an old 4 wire round plug. My truck has the 7-wire trailer outlet for my camper. Does it work and make the most sense to simply take the old 4-wire round out and attach a 7-wire plug, only using the 4 terminals for right, left, tail and ground? Would I leave the other 3 terminals empty? Thanks

asked by: Josh B

Helpful Expert Reply:

Considering that the 4-wire round connector on your Dad's old boat trailer may be nearing the end of its life (due to use and corrosion) you will be better off replacing the 4-way round connector with a 7-way plug such as # H20046 from Hopkins. Installing a new trailer-side male plug will also avoid the complication and cost of having to use an adapter and it will make the trailer much more user-friendly to the majority of tow vehicles likely to pull it in the future.

Installing the 7-way plug will be made easier by using a junction box such as # 38656. This box mounts to the trailer frame and serves as a connection point between the trailer's original wiring and the new 7-way. You will only be connecting to four of the wires in the Hopkins plug. You will need to put ring terminals on all wires; you can use an item like # 44-5356A or a complete wiring kit such as # HM51020.

Please note that wire colors used in this plug may be different than the wire colors used on the trailer. It is best to use a spare 12V battery to test the trailer wiring to confirm what lighting function is carried by each wire. With typical trailing wiring the wires will connect to each other as follows:

Hopkins 7-Way Wire Usual Trailer Wire Color
White White
Red Yellow
Brown Green
Green Brown

The other three wires on the 7-way simply will not be connected inside the junction box.