Parts Needed to add a Battery Charge Wire to a Trailer with a 4-Pin Connector

Updated 04/20/2018 | Published 04/19/2018

Products Featured in This Question

Pollak Black Plastic, 7-Pole, RV-Style Trailer Connector - Trailer End

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$7.45

10 Gauge Wire - Blue Primary - Per Foot

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$1.84

NOCO Genius Smart Battery Charger - AC to DC - 6V/12V - 10 Amp

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$99.95

Wiring Kit for Hydrastar Electric Over Hydraulic Actuators

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Question:

Im looking for a way to charge a battery in a trailer, from my truck while traveling. My truck is equipped with 2 different wire harness options. The trailer doesnt have electric brakes and requires a 4 pin connector. However, I can change the connector if required. The battery in the trailer will only be used for an alarm system.

asked by: Tom D

Expert Reply:

It sounds like you may have a 7-way trailer connector and a 4-way trailer connector on your truck and only a 4-way connector on your trailer. Is that correct? See the attached picture for examples of each.

If this is the case, then this change will be pretty easy. All you will need to do is cut off the 4-way connector on your trailer and add a 7-way, # PK12706, and the appropriate length of 10 gauge wire, # 10-1-1. This will provide your trailer battery with a constant maintenance charge every time your truck is hooked to your trailer. You will just have to connect each of the 4-way wires to the appropriate terminals on the 7-way (see list below) and run the 10 gauge wire from the 11 oclock pin on the connector (when looking at the front of the connector) to the positive post of the trailer battery.

When looking at the front of the 7-way connector (see diagram)

10 gauge wire to 11 oclock pin (battery charge line)
white wire to 5 oclock pin (ground)
green wire to 9 oclock pin (right turn/brake)
yellow wire to 3 oclock pin (left turn/brake)
brown wire to 1 oclock pin (tail lights)

If you want to get really fancy and avoid having to connect wires to the 7-way, you could use our 7-way Upgrade Kit, # HS381-9000. This comes with a 7-way harness, junction box and all of the hardware you will need to give your trailer a clean, factory look. It also gives you the option to add wiring for brakes if you ever want to add brakes in the future or to run multiple 12 volt accessories off of the battery charge wire such as interior lights.

If you want to keep the battery charged while you aren't connected to the truck, then your best bet would be a separate battery charger like the NOCO Genius Battery Charger, # 329-GENIUS10.