Can a 4-Pole Trailer Connector Be Used to Activate Trailer Brakes
Updated 09/30/2025 | Published 02/15/2020
Question:
How do you make the break work on a 4 flat harness
asked by: CARLOS F
Expert Reply:
In order to actuate the trailer brakes, you'd need a brake controller installed in the vehicle and a 6 or 7-way trailer connector. A 4 pole flat wiring harness like the # 18002 you'd looked at carries 4 circuits- right turn/brake lamp, left turn/brake lamp, running lights and ground. The 4 flat connector doesn't have enough circuits nor the necessary wire thickness or gauge to carry voltage to the trailer bakes.
It would seem fairly logical that you could run a wire from the brake lamp circuit to the brakes but that wouldn't work well at all. Every time you hit the brakes or used the turn signal, it would try to full-on operate the brakes instead of sending just enough voltage to do the job like a proportional brake controller would do.
If you'd care to send me details about your tow vehicle- the year, make and model, I'd be happy to make some suggestions for you.
Isabel
9/30/2025
Mike I'm towing a car with u - haul car hauler with a 2023 jeep gladiator . It has a 4 prong wiring and I do have a brake controller. Will the 4 prong wiring help stop u haul trailer? My trailer brake system is not turned on as no 7 prong is hooked up. Question doni have brakes on trailer working? Thank you Isabel
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William
7/11/2024
My son rented a U-haul car transport trailer and towed a car with a 2015 Chevy Silverado. The Internet said this trailer has automatic brakes but has only a 4-pin connector. My son wasn't aware that he needed to have a brake controller installed since his truck had the towing package option. Needless to say he overheated his brakes. I think U-haul misleads the uninformed about this. I cannot understand why a dual tandem trailer designed to haul cars up to 5800 lbs. does not have a 7-pin connector to control the brakes albeit my son's truck needs a brake controller installed as well. Any constructive comments appreciated.