Trailer battery not charging from tow vehicle

What size is in it now? Check the fuse with a multimeter and check the 7 pin connector at the bumper for power.

Common problem these days. The problem is lower (than older vehicles) voltage being generated by the vehicle (around 13.5V) and voltage drop in the circuit back to the TT battery. The TT battery is probably seeing 13.0-13.2V, not enough to charge a TT battery that is low.

I have yet to see a good, simple solution !

The first thing you need to do is see if you have power at the 7 pin/pole connector at the bumper.

IIRC, there are fuses in the main fuse bus panel that can interrupt power to the trailer connection. They are mini fuses. There may also be a fuse in the engine compartment relay/fuse box that is in the trailer "charge" connection circuit. It's been awhile but those two locations are the only ones I remember as being in the trailer connection circuits.

Alaskan Fly Guy wrote:
My travel trailer does not seem to be charging from the tow vehicle while traveling. I think I may have a bad 20A fuse for the "tow battery charge". There are 2 choices for these fuses. A tall one and a shorter one. Which one do I get for my 2003 F-250? Thanks in advance.

Which ever 20 amp fuse will fit properly; same size electrically and physically as what's in there now.

BUT....words like "seems to be" and "I think" indicate that you are going about this wrong.

Get a multi-meter and check the fuse and then check the voltage on the charge line at the trailer and then at the trailer's batteries. Then you will KNOW what the situation is and won't have to guess, at least not so much.

Not sure about yours, but my 2007 F150 needed a relay to activate the 12v charge line. Supposed to be in the glove box when the vehicle was new, but I had to purchase one at auto supply store.

You didn't list the year and/or make of the truck so this may not be applicable. My '05 Chevy had a dummy fuse in the fuse box under the hood. It had to be replaced in order for the power to get to the pin connecter. I guess some people never tow so they don't need the power source. It was just a piece of plastic in place of a fuse.