Troubleshooting Trailer Brakes That Lock Up When Trailer Connector is Connected

Question:

what would make the brakes lock up on a eletric car tiler breaks lock up when you plug the trailer in to the truck... the truck does not have trailer breaks... we have traced the lines and they are all factory lines ran nothinghas ben changed...and what shouold the battery be at when the tailer is pluged in to the truck.

asked by: Michael W

Expert Reply:

It sounds like the 12 volt accessory circuit on the trailer connector of your tow vehicle is shorting out to the brake output circuit on your trailer and which is causing the brakes to lock up. Check the connector for corrosion on the inside and outside, cut or exposed wire and fix as necessary.

Also, use a circuit tester like part # PTW2993 to test the functions of the 7-way on your vehicle and compare them to the chart I attached to make sure every thing is wired up correctly.

If you are asking what voltage the battery on your trailer should be at when fully charged it should be at 12 volts. If you are asking how it should be wired, the 12 volt circuit from the trailer connector should be run to the positive post of the battery.

expert reply by: Jameson C