Trailer Brakes are Weak Unless Breakaway Pin is Pulled

Updated 04/13/2018 | Published 04/12/2018

Question:

My breaks work fine when the breakaway pin is pulled . However breaks are very weak when both the brakes and controller are applied at the Max setting . I have 13.5 V at the 7 pin connection on the truck when the break AND the controller are applied . I have also replaced the 7 pin connector , breakaway , switch , all 4 brakes on the trailer . Still have weak breaks when towing .

asked by: John B

Expert Reply:

If you are registering 13.5V at the 5 o'clock pin on your truck side 7-Way (see attached picture), and your trailer brakes fully applied when you pull the breakaway pin, that leads me to believe the problem is in the wiring between the 7-Way connector on your trailer and where your breakaway battery is connected.

Check to make sure that your connector is clean and free of dirt and corrosion. If the 7-Way that you replaced is on your trailer side then this should be good to go. Next inspect the wiring between these 2 points and look for anything that looks damaged or pinched.

After that the only other thing that I can think of is to check your grounds to make sure they are secure and connected to clean, bare-metal surfaces. Typically, weak brakes mean that they simply need to be adjusted, but if they are locking up when you pull the breakaway pin that means they are properly adjusted.

If this troubleshooting doesn't help you then your next best bet would be to take your rig to a trailer shop so that they can physically inspect it for you. It sounds like you have done a significant amount of troubleshooting so having someone else who also knows what to look for might yield some results.

expert reply by: Jon G