Installing Connector on Trailer with Electric Brakes and Battery Wire

Question:

All wires except my purple trailer brake are hook up and the black battery one where does the black wire go on a 4 flat?

asked by: Gregory J

Expert Reply:

A 4-Way flat trailer connector like # HMC20031 does not have a pin/circuit for the 12V battery wire. A 4-Way like this will only work to connect with another 4-Way on the tow vehicle so that the trailer's basic signal lights (brake light, turn signals, running lights) are powered.

If your trailer is equipped with electric brakes and you need the 12V wire to maintain the charge on a battery (or power a 12V accessory) then you will need to have a 7-Way connector on both the tow vehicle and trailer. It sounds like the trailer is already all wired up for this so it's just a matter of using a 7-Way like the Pollak # PK12706 instead of the 4-Way you are trying to install. I have attached a wiring diagram on this connector that you can use for reference.

If you can tell me what model tow vehicle you have I will be happy to recommend a 7-Way harness if it's not already equipped with one.

expert reply by: Chris R