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Electric Brake Terminal on 7-Way Connector is Showing Constant 12 Volts Under All Conditions

Question:

Should there be any voltage on the EB Electric Brake terminal of a 7 way plug when the vehicle is parked and all power turned off? It registers a solid 12V under all conditions. Something is draining my battery when the trailer is hooked up to my vehicle and parked.

Expert Reply:

On some vehicles, the key has to be on for voltage to go back to the trailer connector. On others, it does not. An electric brake controller will always send back some minimal voltage to the trailer connector. This is how it senses if there is a trailer connected.

But it should not be showing 12 volts all of the time. If it is on the brake pin, 5 oclock position if looking at the face of the 7-Way, then that indicates that there is a short to the brake wire. If the 12 volt power is showing on the pin in the 1 oclock position, then that is the 12 volt circuit and it showing 12 volts all the time is not uncommon.

There can be a couple of things that can cause a short to the brake wire. If the brake controller was miswired, that can cause the problem. On a brake controller, the white wire is ground, the black is 12 volt power to the controller, blue is output to the trailer connector, and red is in from the stop light switch.

Depending on what brake controller you have, if the truck came with a factory 7-Way trailer connector, you could just use the wiring harness to plug into a factory connection point on the truck. This will eliminate any potential miswiring with the brake controller.

You can also test the blue wire on the back of the brake controller. If it shows constant output then chances are there is a problem inside of the brake controller and it will need to be replaced. If the controller was hardwired to the vehicle, make sure the ground is connected to the negative battery terminal.

You will also want to make sure that the trailer connector is free of corrosion inside and in the back of the connector. If a 7-Way was added as an aftermarket part, make sure that the white wire is grounded to the truck frame.

I am including a link to a FAQ page on trailer wiring.

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