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Equipping 2004 GMC Sierra to Maintain Battery on Enclosed Trailer


Ok there are a lot of ways to connect a standalone battery to a enclosed trailer but I am trying to figure out the best way that is industry standard for both the truck safety and trailer. Here is what I have..2004 GMC 3500 Sierra Dully with a 7 pin trailer plug. I have a 2006 Pace Pursuit trailer with 12 volt and 110 volt wiring system. I am adding a battery to the trailer so when the trailer is unplugged I have lights that work without starting up the generator. I want then truck to charge the battery as I am driving but in dual battery setups you use a isolator so you dont over charge or under charge either battery. So if I use the 10 gauge wire that is the 12 volt source in the 7 pin plug and wire it directly to the battery dont I run the risk of not properly charging the trailer and truck battery? Also if I have the trailer harness plugged in and the truck is off then I will be draining both batteries in the event the 12 volt lights were left on or were being used for a long period of time. So with that said what is the best way to wire that battery into the system? I was thinking of a continuous duty solenoid to activate the trailer battery wire to get charged but still possibly need a battery isolator and a trigger switch in the truck since you will need to activate the solenoid. I want to try to keep this as simple as possible and not have to run any more wire to my truck. I dont mine rewiring a few things on the trailer. I am adding your junction box so I can break out and wire some backup lights I just ordered from you. Any help and diagrams would be great. I am well diverse in electrical but looking for the best way to do this. Thanks for any help you can provide I am sure that I am not the first person that wants to do this and has these questions.


Expert Reply:

What you are wanting to do is actually pretty simple. The 12-Volt accessory circuit on your 7-way can be used to tend or maintain your battery on your trailer, but the circuit does not have sufficient amperage to charge a battery that has been completely discharged.

Using a battery isolating solenoid like part # TR118665 would be advisable. This will prevent the battery on the tow vehicle from being discharged by disabling the 12-volt accessory circuit from the 7-way once the ignition on the truck is shut off.

We have a diagram showing how to wire a battery used to power a trailer mounted winch, the principle would be the same for what you are wanting to do. Click on the 'helpful link' icon to see the diagram.

expert reply by:
Mike L

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