Can a Larger Breakaway Battery Be Used to Operate Interior Lights On a Trailer

Question:

want to change out small brake breakaway system battery for big batterie that will work interior lights as well as breakaway brake system. Can i charge this full size battery with 12 v suply from my truck with out problems? Worried about back feeding my truck!. Any help advise you can give would be greatly apreiciated. Thank You!

asked by: Ryan W

Expert Reply:

You will want to use a separate, standard 12 volt deep cycle trailer battery to operate the interior lights. You will NOT want to use the trailer breakaway battery. The breakaway battery is not designed to power other trailer accessories or lighting, it is just designed to operate the breakaway system. The DOT regulations state that a trailer breakaway system needs a dedicated battery.

You will be able to maintain a charge on the separate trailer battery by running a 10 gauge power wire like the, part # 10-1-1, from the 12 volt power pin (# 4 terminal at 11:00 position) on your trailers 7-way connector, to the positive terminal on the trailer battery. Now when the trailer is connected and you are towing, the tow vehicle will provide a maintenance charge to the trailer battery. It will not charge the battery from a discharged state.

You will want to test the # 4 terminal at the 1:00 position on your tow vehicles 7-way connector for power with a circuit tester, like part # PTW2993. This is the terminal that will supply the 12-volt power to your trailers 7-way connector. If it does not show power, you may need to insert a fuse and/or check that the wire is connected to a power source by tracing the wire back.

I am sending a link to a FAQ page on trailer wiring diagrams, which will show the 7-Way connectors and which pins are for what functions.

expert reply by: Jeff D