Blowing Fuse for Trailer Brakes Troubleshooting

Updated 10/27/2025 | Published 05/14/2025

Question:

Fuse blows on trailer brakes? Ive isolated all 4 brake 2.8 ohms on left side and 3.8 ohms on right side, 1 ohms at plug. Checked all wiring and connections for shorts to ground. Checked magnets to ground, no shorts anywhere. Im at a loss what else to check or consider. Thank you Gary

asked by: Gary C

Expert Reply:

Hi Gary, thanks for reaching out. You're doing all the right things so far, and I totally get how frustrating this can be. Your brake resistance readings look good, 2.8 ohms on the left, 3.8 on the right, and about 1 ohm at the plug. (which is low) You've checked for shorts, tested the magnets, and looked over all the wiring, great work so far.

At this point, I'd suggest checking the amp draw under load. Each brake magnet should pull around 3 amps, so 12–14 amps total. If you're seeing more, that could be what's blowing the fuse.

Another thing to check is the breakaway switch, If the switch is faulty or the pin isn’t fully seated, it could be sending full voltage to the brakes constantly, which would absolutely blow a fuse. Make sure the pin is properly in place and that the switch is working as expected.

I know you mentioned checking the ground already but make sure it is attached to a clean bare metal surface of the trailer's frame. Sometimes paint can cause a bad ground.

Please let me know how it goes!

expert reply by: Heather A

Heather A.

9/29/2025

Hey Gary, did you have a chance to check the amp draw under load or take a look at the breakaway switch? I'm eager to hear how it worked out for you, as it might help others facing a similar issue.

Gary C.

9/30/2025

@HeatherA I don't know how to check under load. That would be while driving? I've separated the whole wire harness twice now. Test continuity and to ground. Tested ohms to each magnet individually and tied in parallel. I applied power to each magnet and they did magnetize. I didn't check ohms when powering the magnets. That maybe what you are referring to. The system is still blowing fuses. Thank you for your follow-up

Heather A.

10/27/2025

@GaryC Sorry for the late response Gary. I started on a different project and didn't realize I was still getting replies from customers so again I apologize. You would want someone to engage the brakes while you test the wires. You would need a buddy to pull or slide the manual override. When a trailer keeps blowing fuses for the brakes, it almost always means there’s too much current draw or a short to ground somewhere along the blue brake wire.