Troubleshooting Vehicle Battery Drain After 7-Way and Brake Controller Installation

Question:

Hello I have a 2013 volvo xc60 which we had a 12v 7pin installed as well as a reliance brake controller. Since the installation of both my car battery has been needed to be replace 2x. Today at the local dealer the tech said that inch the aftermarket charger was drawing the max amount from my batter. inch He disconnected a wire that went from my battery to a junction box that had been installed into my fender. He said when he disconnected the wire the draw load on my battery ped by 3 points. He, however, is unable to tell me if he disconnected a wire from the 7pin set up or the break controller. Does the 7pin pull from the car battery even when it is not attached to the trailer? Does the break controller constantly pull from the car battery ? thank you

asked by: Lexie

Expert Reply:

The 12V power circuit in an aftermarket 7-way connector like # 37185 will usually be connected to the vehicle battery through a 40-amp circuit breaker like # PK54540. This installation provides for 12V power at the connector contact at all times, even when the vehicle is off and even when no trailer is connected. Vehicles that have OEM wiring could be set up differently so that the ignition key controls the 12V feed to the trailer socket.

Trailer brake controllers do draw some power at all times, but unless a trailer is connected this is a tiny amount of power that would require several months to deplete the vehicle battery. Brake controllers usually have LED power indicators to let you know they are receiving power but these small LEDs draw so little power that in normal use there is no need to unplug the controller when it is not being used; plus this is risky since it is possible to forget to plug the unit back in when towing the trailer. This is why trailer brake controllers do not have power buttons to let you turn them off.

It is possible that you have a parasitic short on that 12V power circuit. Something as simple as the 12V circuit wire rubbing on the frame (of the car or trailer) could cause the vehicle battery to be depleted. The brake controller could drain your battery only if it has suffered internal damage. Another possibility is that either the vehicle's socket or the trailer's plug has internal corrosion that is allowing the 12V circuit to bleed over to another. When adjacent circuit pins develop corrosion power can bleed over to another circuit.

I suggest you connect a quality AC-powered battery charger like # CTEK56353 to your Volvo battery and give it a full charge. Unplug the brake controller so that it can be eliminated as a potential cause for the battery drain (or you can cut the black 12V power wire if you cannot unplug it) and unplug the trailer too to eliminate it as the source of the problem.

If the battery drain problem continues you can test the car by itself (with the brake controller and trailer NOT connected) by applying a simple circuit tester like # PTW2992 to each fuse in the power box. This test will let you see if any circuit on the vehicle is drawing power when it should not be. This is a basic test most auto shops should be able to do in not too much time.