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Will a Trailer Drain the Battery on a 2009 Ford F-350 if the Trailer Stays Plugged In


On the 7 way trailer connetors the black 10 gage wire is labled for battery charge. What keeps the trailer from discharging the truck battery should you run the trailer battery low. This is on a 2009 Ford F-350 Super Duty. The trailer is just a run of the mill car hauler with a group 24 battery for the lighting and a winch.


Expert Reply:

On some vehicles, the 12 volt circuit will not be hot unless the key or engine is turned on/running. Test the 12 volt pin on the 7-Way with a circuit tester like # 40376 if needed to see if the 12 volt circuit is hot all the time. If it is, the easiest solution is to unplug the trailer when the vehicle is off.

Another option is to install a battery isolation solenoid # TR118665. For this you would run a lead from the positive battery terminal to the input of the solenoid. Then you would run a power wire from the output side of the solenoid first to a 40 amp circuit breaker like # PK54540 and then from there all the way to the back of the 7-Way. You would then replace the factory 12 volt wire with the new one. The center terminal on the isolation solenoid will need to be attached to a 12 volt ignition source so it will only allow power to flow through when the ignition is on.

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