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Solenoid Recommendation To Prevent Trailer 12 Volt Acc Circuit From Being Active When Key is Off


Hi, I have a 20x8.5foot Enclosed car hauler with electric brakes and a breakaway battery that I tow with my half ton. I would like to add an auxiliary battery in the trailer that will do the following. 1. Be charged by the vehicle when connected to the vehicle with the 7 way plug already in use. 2. Not back feed or drain the primary vehicle battery. 3. Use 12v accessories such as: LED Lighting, Winch etc. 4. Use 120v items such as a drill, air compressor or maybe even a small electric heater. I have the feeling I need some sort of solenoid or isolator to do this. I would like to know what products I would need to accomplish this, and perhaps a quick diagram if the time allows. Thank you -


Expert Reply:

We have just what you need. To prevent the vehicle battery from being inadvertently discharged, you can make sure the trailer is unplugged when the vehicle is turned off or you can install a battery isolating solenoid like part # TR118665. The solenoid would be wired according to the photo I edited for you.

When the center pin of the isolator is wired to an ignition powered power source (a circuit that only has power when the ignition switch is turned on), the power feed will only be active when the ignition is turned on. IF wired correctly, the solenoid will automatically power the circuit up when the ignition is switched on.

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expert reply by:
Jameson C

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