How are a Trailer Brake Controller and Brake Away System Related and Connected

Updated 10/14/2013 | Published 10/12/2013

Question:

Describe the circuit which allows the trailer emergency brake to function while letting the brake controller to control when connected. With the truck not connected I detect trailer battery voltage at the trailer connector. This voltage drops slightly when the emergency trailer disconnect is activated, due to brake activation. I dont have a circuit print for the trailer.

asked by: John

Helpful Expert Reply:

Some of this information might be a review but bear with me. Some trailers have what is called a break away kit. Basically, this kit is wired in line with the braking system. There is a switch that has a pin in it. The switch is mounted to the trailer. The pin has a cable on it that connects to the tow vehicle. If the trailer breaks away from the tow vehicle, the pin pulls out. With the pin out it allows 2 metal contacts to touch, completing a circuit from a battery on the trailer to the trailer brakes. This engages the trailer brakes and slows the rouge trailer.

If we follow the path from the vehicle to the trailer brakes it starts at the brake controller. That leads to the vehicle side 7-Way then to the trailer connector. From there the brake signal goes through the break away system and ends at the trailer brakes.

If there is a brake magnet or wiring short on the trailer side, it can back feed to the vehicle side and could cause some problems. If there is a short on the vehicle side it could be sending power back to the trailer when it is not supposed to. A brake controller sends back a small amount of power to check for a trailer. That is how it knows a trailer is connected.

I have included some FAQ article links on installing and testing break away systems, troubleshooting brake controllers, and testing brake magnets for you.

expert reply by: Michael H