Trailer Brakes Not Working but Other Trailers Work Just Fine with Truck

Updated 03/20/2018 | Published 03/18/2018

Question:

I have two trailers that when plugged in show as connected on my brake controller and the electronic brakes work as they should. I am looking to troubleshoot a Boy Scout Troops trailer that when connected does not show as connected on my controller and the brakes do not activate . I am pretty certain the issue is the trailer side since my two trailers work with my vehicle / brake controller. Whats the process I should follow to eliminate issues? Thank you!

asked by: Eric

Expert Reply:

You're probably right that the issue is on the trailer side since other trailers work with your truck. First start by checking the connector of the trailer and making sure the pins are clean and in good shape.

What you can do to test the trailer is get yourself a 12 volt battery and connect each pin on the trailer's 7-way to the positive pole while grounding the negative pole one by one. Doing it one by one tests each function individually just to go through them all. It also tells you if the trailer is wired correctly and you don't have something connected to the wrong pins. I've attahed a wiring article to help you identify what each function should be. The brakes should lock up when connecting the pin in the 7 O'clock position to the battery.

If everything, including the brakes, work on the trailer when testing with the battery once you identify which pin each function is you can use a circuit tester, like part # PTW2993, and test each pin on your truck for function. What I'm thinking is possible is the trailer and truck are not pinned the same. Especially since you said the trailer belongs to a scout troop which means there's a good chance the trailer has been towed by many different people and many different trucks. My son's scout troop's trailer has this problem. So, it turns out only two guys can pull the trailer since their trucks just happen to be pinned the same as the trailer.

If the issue isn't in the connector, then it's probably in the wiring or the brake magnets. Inspect the wiring back to the brakes and inspect the magnets themselves. With the trailer connected to power you can use the circuit tester on the brake circuit and trace it to see when it stops getting power to isolate the issue. If the magnets are bad, they can likely be replaced. Or you can replace the brake assemblies themselves. Let me know the drum size and I'll make a specific recommendation for you.

expert reply by: Charles S