Charging a Trailer Battery Using a Battery Isolation Solenoid # PK5231201

Updated 04/25/2013 | Published 03/24/2011

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

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$35.05

Hook Probe Circuit Tester

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Question:

Can I mount the Tow Ready Battery Isolation Solenoid on the trailer in the accessory wire from the 7 pin harness that would be used to charge the trailer battery. And then use one of the other switched wires in the harness for the ignition wire instead of hooking directly to the batteries?

asked by: J.O. S

Expert Reply:

If there was a wire in the harness that you found that was also a keyed power source (meaning that it has power when the key is on, and none when the key is off) you could wire it up the way that you described, but traditionally at a 7-Way connector there is not a wire that has voltage when the key is turned on and none when the key is turned off, unless it is the 12 volt power source. It just depends on the vehicle whether or not that circuit is keyed or not.

First thing I would do is use a circuit tester like part # PTW2993 and see if the 12-volt power source on your 7-way connector has voltage all the time or is only powered when the key is on.

If it only has power when the key is on, then you have found your keyed power source. If not, then you will need to find a wire that is on the ignition circuit to turn on the Battery Isolation Solenoid, part # PK5231201.

expert reply by: Jameson C

Christo

4/2/2013

I have a 2011 ford F250 with stock tow package. the 12v in the 7-way on fords are only hot when the key is in ON position-So my question can I use the 12v switched from the pickup to the isolator that will be hooked to a 12v battery charger and the ignition circuit to turn the isolator on?

Patrick B.

4/25/2013

Perhaps I am missing something, but if the 12V circuit is only hot with the key in the on position, there is not really need for the isolator. The isolator is used for setups where the 12V is hot all the time. The isolator then breaks the connection when the key is off so the trailer does not drain the truck battery.