Troubleshooting Battery Drainage After Trailer Brake Controller Installation

Updated 03/12/2018 | Published 03/10/2018

Question:

I checked the wiring on the plug at rear of truck and everything is good. I have a brand new brake controller installed and tried another new one with the same problem green light stays on. I also checked the wires from the brake controller and all are correct BLACK BLUE RED WHITE ON BOTH ENDS OF THE CONTROLER PLUGS. If I move the lever on the brake controller the green light gos off and changes to a orange color. If I leave the brake controller plugged in the Batt. will go dead. If I unplug the brake controller the Batt. will stay charged. I dont know what to do next.

asked by: Ron

Expert Reply:

Trailer brake controllers are meant to remain powered up at all times. This avoids the risk of forgetting to turn the controller on when towing. This is why they do not have on/off power buttons.

The small LED light on a trailer brake controller will not draw enough power to drain a vehicle battery. This might become a concern if the vehicle were to be left for many months continuously, without ever being started, but it is not an issue in normal use.

If your vehicle battery is draining I suggest you carefully inspect your 7-way connector and the harness/plug connected to it for any signs of damaged contacts or corrosion.

What can happen is that corrosion can build up inside the socket, on the connector that plugs in to it, or elsewhere in the wiring. It can often be very hard to spot this corrosion when it happens inside a connector. But if moisture gets trapped inside it can develop into a corrosive build up that can actually bridge/join two adjacent circuits and cause a short that could drain your battery.

For instance, if you look at the linked photo of a 7-way vehicle socket you will note the 12V auxiliary power circuit (that powers trailer lights and maintains a trailer-mounted battery) is at the 1-o-clock position. Corrosion inside the connector could cause this circuit to short to ground which would drain a battery.

If you have a circuit tester like # PTW2993 you can apply it to the various circuits on your 7-way to check for power leaking onto circuits that should not have it.

expert reply by: Adam R