How To Wire Larger Deep Cell Battery On Trailer To Be Recharged From Battery On 2008 Dodge Ram 2500  

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If you are wanting to put a larger deep cell battery in your trailer to power your winch and recharge it from the battery on the 2008 Dodge Ram 2500 you will need to wire it directly with the Wiring Kit, # BDW20043, depending on what size winch you are using.

The Wiring Kit, # BDW20043, has 16 feet of 3 gauge double wire to run from the rear of the vehicle to the front. I checked the length of 2008 Dodge Ram trucks and the overall length of the longest truck was 25 feet. So you might want to measure on your truck to see if the 16 feet will work on your vehicle.

I also have the Trailer Wiring Kit, # BDW20207, which has a heavier 2 gauge wire for bigger winches and it has 24 feet of double wire.

You can also connect your breakaway battery on your trailer directly to the larger deep cell battery by connecting the black 12 volt power wire splicing to the positive wire on the larger battery and the white wire will be attached to a good ground. The remaining blue wire will be connected to the brake output circuit on the trailer.

When wiring a trailer battery for charging using a 7-Way trailer connector you will only be able to maintain a charge, it will not allow you to recharge a larger deep cell battery.

If you are wanting to maintain a charge on your breakaway battery in your trailer you will need to connect the positive wire from the breakaway battery to the 12 volt power wire on the 7-Way trailer connector. It will attach to the wire coming from the top right pin (if looking at the back of the plug) on the 7-Way to the breakaway battery positive terminal. Now when the trailer is connected and you are towing, the tow vehicle will provide a maintenance charge to the breakaway battery.

On your 2008 Dodge Ram 2500 if you are trying to maintain a charge for a trailer battery via the 7-Way, you will want to use the top right pin on the 7-Way (if looking at the front of the vehicle side plug). It is the 12 volt power source and uses a black wire.

You will want to test the black (12v power) wire on your vehicles 7-way connector to make sure you have power going to the connector. If your 7-Way vehicle side is not providing 12 volt power, you will need to check that the wire going to the top left pin at the back of the plug is connected to the vehicles battery positive post.

Also, check the fuse box under the hood to make sure that the fuse is good. If you remove the cover and check the label on the underside of the cover it should list which fuse is for which function.

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

expert reply by: Jeff D

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