2012 Ford F-350 Battery Draining When Connected to Trailer Over Night

Updated 05/09/2016 | Published 05/08/2016

Products Featured in This Question

Starter Solenoid - SPST - 12 Volt - 100 Amp - Continuous Duty - Grounded

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$35.41

Hook Probe Circuit Tester

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$14.40

Question:

I have an 2013 Aluma AE722TA with an auxiliary battery to run the interior lights without truck hooked up. My truck is a 2012 Ford f350 with built in brake controller, when the trailer is hooked up and left over night and the truck is off, it drains the truck battery, all lights are off in the trailer. What would cause that?

asked by: Frank E

Expert Reply:

If the 12-volt tow package circuit on the truck has power all the time, even when the truck is turned off, then it could be feeding into the trailer mounted battery causing the truck battery to drain. You can use a circuit tester such as # PTW2993 to test the 7-Way on the truck to see which pins, if any, have power when the truck is turned off. If the pin in the 1 o'clock position does have power with the truck off, then that would be the issue. Easiest solution is to unplug the truck and trailer.

The other option would be to install a battery isolation solenoid, # PK5231201, in line with the 12-volt circuit wire. The center post connects to a 12-volt ignition source (something that only has power when the key/truck is on, such as the radio). When the key/truck is turned off power to the 12-volt circuit will also be turned off.

It is also possible that there is a corroded trailer connector that is causing power draw. Make sure the truck and trailer side connectors are clean and free of corrosion inside, where the wires attach, and outside on the pins. Also check the wiring to and from the battery including the ground connections and make sure there are no pinched or damaged wires or corroded connections.

expert reply by: Michael H