How to Upgrade 4-Pole Wiring to Allow Use of Trailer Reverse Lights

Updated 05/16/2018 | Published 05/15/2018

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Question:

I want to add reverse lights to my boat trailer. I purchased lights that have a Red and a Black wire. Which wire goes where? I expect I will need to buy 12 or 16 wire to run to a 7 pin connector as the trailer is only a 4 pin now. In reviewing most pictures of trailer wiring they appear to only show a single wire.

asked by: Jay T

Helpful Expert Reply:

If the reverse light you are adding to your boat trailer is a single-function light like # BUL002CB (not a combination tail and reverse light like # STL68RB) and it has two wires, red and black, it should not matter which one you connect to ground.

This is easy enough to check just by briefly connecting the light wires to your vehicle's battery; try it both ways (red to battery positive and red to battery negative) and see if it functions the same way with both wiring options. If it is a single-function light it should.

You are correct that you existing 4-pole wiring does NOT support the reverse light function. You will need to add one more circuit to the trailer's wiring to add the backup light function. You could upgrade the whole trailer to 7-way wiring with a junction box like # e99009 paired with a # H20046 standard RV 7-way cable, but you can also just add one circuit using a 4-pole to 5-pole adapter # 47515.

This adapter connects to your vehicle 4-pole wiring and includes an additional wire and quick-splice connector that allows you to connect that new wire to your reverse light circuit. The one new wire will need to be extended using # 12-1-1 to run back to the trailer's new reverse lights.