4-Pole, 5-Pole and Wishbone Style Trailer Wiring

Question:

Trying to wire tail lights on a 4 wire connector from a 5 wire connector

asked by: Ed I

Expert Reply:

There are two types of 5-wire flat trailer wiring harnesses; the wishbone style of 4-pole such as # A35W42B which has 4 pins but that has two separate wires connected to the the running light pin so that you have one wire for each side of the trailer; and the 5-wire 5-pin type like # HM47910 which actually has 5 pins, one being for an additional circuit such as a trailer coupler's electric reverse lockout feature.

The basic lighting on a trailer requires only a 4-pole hookup; this 4-pin wiring has a ground and three circuits: 1) left stop/turn, 2) right stop/turn and 3) running lights. The 4th pin/wire is the ground that support all three of those circuits. You can refer to the linked article on trailer wiring for more details about wiring formats.

If your vehicle and trailer each have different connectors, one a 4-pole and the other a 5-pole, they can still connect. The only thing is that the additional circuit will not be connected. If you want a 4-pole to 5-pole adapter we do offer these such as # 20036 and # 47515. These have an extra wire that connects to the vehicle's reverse light circuit to operate the trailer coupler's electric lockout feature.

expert reply by: Adam R