Six pin trailer hook up.

OK here is the deal, I am buying a trailer with a six pin hook up. i have a converter to go from the 4 pin plug (which I have hooked up with a kit from the dealership) to the six pin so I am good to go with the lights. But I still need to run a 12 volt from the car to the plug so I can charge the battery from the car while its hooked up during towing.

My questions has anyone done this?? If so where is it best to run the wire from? I have no problem running wire but I just want to know if it would be better to run something from the fuse box or tap something in the rear?? Any help would be great...


Boss