I want to add battery to my horse trailer to power exterior lights and what not. My intent is to use the center pin of the 8 pin connector to charge the battery while I am driving.

How do I wire this so that the battery charges while I am driving and does not drain my truck battery while I am parked?

 

If you have the tow package on a late model Ford, it only charges when ignition is on. Otherwise, find the wire from the truck battery to the center(charge) pin on the trailer connector, and cut it and run it thru a relay. Wire the relay to any point that's hot when ignition is on. And you might want to add a fuse or c.b. in the charge wire while you're at it (if it doesn't already have one).

 

I'm curious as to what you finally come up with. I'd like to do the saem for my CM Endurance trailer. But am a bit unsure of a few things.

Maybe you've already addressed these things.

1. How do you wire it so that only the accessories get the battery power and not the taillamps and such?

2. What size battery are you going to use?

3. Are you going to put a main "switch" to turn the batery power on and off?

 

I do have a 05 F350 PSD with the tow package. Can I just run a fused wire from the center pin to the battery? Is is that simple? What gauge wire and fuse should I use?

For the acessories I plan on rewiring them to the new battery.Tail and turn lights will remain the same.

As far as the battery goes I am not sure yet. I only plan on running a couple lights. Maybe a deep cycle/starting.

 

No fuse needed, it's already fused, and only hot with key on. Use #12 wire for small to medium battery, #10 for big deep cycle batteries. Should work fine.

 

The 7 pin trailer plug already has a 12V hot wire that is switched to turn on and off with the engine. Why not use that?

At least my '04 is wired that way..

 

Hummnnn, thought I said that......

 

The seven plug has a 12V trailer charge already, will be pin 4. Here is a website that has the standard wiring for trailer. The center pin on the later fords is tied in with the BackUp lights. i.e. the center pin will be at 12V when the truck is in reverse. Also while on it. I'd highly recommend wiring your trailer to the industry standard. If not may cause problems for the trailer or another tow vehicle if used by another.