Trailer brake trouble

I spent most of the day running a new wiring harness on my father in law’s trailer so I can haul a tractor this spring. During the work, I found out that it has brakes. So I wired in a controller that I had courtesy of @Vbb199 and put a 7 pin connector on the truck and trailer. Now, as far as I can tell, everything on the truck side is right. I have running lights, turn signals, and brake lights. Brakes seem to work also. But when I turn the four way flashers on, it activates the brakes every time the lights flash. I can stand next to the trailer and hear them activating. It ONLY does this with the four ways on, not left or right turn signal only. Also, when I activate the controller manually, I noticed the brake lights on the trailer lighting up as well. Any ideas? This is my first go around with trailer brakes, and I’m stumped.

Sounds like your electric brake controller trigger is wired to the wrong wire. Should be wired to the cold side of the brake pedal switch. If you have a trans with a locking converter there will be two brake pedal switches. Make sure you tap into the switch for the brake lights and not the trans converter.

Yes, when you push the panic bar on the controller, the brake lights should light.

The last possibility is the trailer light circuit has a a bad ground, either on the truck or trailer.

I have a manual transmission, and I verified that I tapped into the cold wire on the brake light switch. The trailer should have a good ground. Well, it did while I was testing. I ground the paint off for good contact and put a new terminal in with a bolt. Same for the truck side, bolted to bare metal for the best possible contact. But after I moved it, the ground wire pulled loose because I didn’t leave enough slack. I forgot to mention in my first post that the trailer brakes had two wires. After looking at a couple diagrams, it seems one side goes to the plug to interface with the controller, and the other wire goes to ground. So that’s how I hooked them up. Could be incorrect information though.

Maybe at the trailer plug you have the wires for the brake lights and the trailer brake magnets reversed?

After the first test I didn’t have tail lights. I pulled both plugs apart and had two wires crossed up on the truck side. Fixed that, and double checked the trailer side. Everything looked good there, but I’ll check it again when I start back in on it.

Well just to update, I pulled the trailer with a load on it yesterday and the brakes worked perfectly. I didn’t try the four ways to see if they are still activating the brakes. It’s still hooked up so I’ll do that in a bit. But, I have at least confirmed that everything is wired and operating properly.

is this one of those old hydraulic line to the controllers ones?

AuroraGirl said:

is this one of those old hydraulic line to the controllers ones?

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No it’s a newer all electric one.

I was gonna say, the old ones i couldnt see how the issue would happen but newer one i could see the potential. but you seemingly have it figured out? Or does it still act weird

AuroraGirl said:

I was gonna say, the old ones i couldnt see how the issue would happen but newer one i could see the potential. but you seemingly have it figured out? Or does it still act weird

Click to expand...

Trailer brakes work perfectly. But it still applies the brakes when the four ways flash. Instead of the brake pressure rising on the display, it just shows a constant 5% activation. So the display flashes 5 whenever the four ways flash. You can also hear the brakes pulsing if you stand beside the trailer. But other than that they work as they should.

I would look at EMI and possible insulation to remedy it
Try switching flasher and four ways and use your turns