How To Maintain a Trailer Battery Using A 7-Way Trailer Connector On a 2008 Nissan Pathfinder

Question:

I use a 7 pin connector when towing a trailer with electric brakes. everything works except the trailer battery does not charge. is there a fuse in the Nissan I need in order to charge the trailer battery while towing?

asked by: joe

Expert Reply:

You will not need a fuse to charge your trailer battery while towing. 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.

On the trailer side connector, attach the wire coming from the top right pin (if looking at the back of the plug) to the trailer battery positive terminal. Now when the trailer is connected and you are towing, the tow vehicle will provide a maintenance charge to the trailer battery.

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 vehicle battery.

You will also want to check under the hood in the fuse box to make sure you have the brown relay installed in the fuse box. This relay will activate the 12 volt power circuit. It might be already installed from the factory. If not, the relay is included with the part # N40975.

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