Battery Charging to a trailer

jimpaget · Mar 7, 2014

I am going to be mounting a winch on my trailer for use in emergency loading situations. I would like to be able to charge the battery from the charging lead in my wiring harness from the tow vehicle to the trailer.

Will I need to have a battery isolator?

In any case, what would the wiring schematic look like?

ChopTop84 · Mar 7, 2014

If your truck is new enough, the charge wire is already there (on a 7 pin big round connector anyway), and if you have trailer brakes and a breakaway switch on your trailer, the trailer end should be wired for charge already also.

The truck *MAY* need a relay installed under the hood, along with a fuse. Depends on model year and package. Fords came with a bag in the glovebox that you installed yourself that had all the parts already.

Otherwise, its automatic. When truck turns on, it activates the relay and starts charging the battery at about 10 amps of power. When you turn off the truck, it disconnects the charge relay and no worries about isolation.

Charge wire should be Pin #4. Black wire. 10 gauge.

zukkev · Mar 7, 2014

His is a 97, like mine...
yes, the charge wire should already be there Jim...And yes, the relay supplying power to the plug will turn off with the key---no isolator needed...:awesomework:

jimpaget · Mar 8, 2014

I should have been clearer in my question. I was concerned with whether or not I needed to isolate the battery for the winch and the battery for the trailer breakaway battery.

ChopTop84 · Mar 8, 2014

jimpaget said:
I should have been clearer in my question. I was concerned with whether or not I needed to isolate the battery for the winch and the battery for the trailer breakaway battery.

Delete the break-a-way battery, and wire direct to your winch battery. Its a better battery anyway, and odds are good your break-a-way battery is toast, as they dont last long. You just dont know it yet.

Totalled · Mar 8, 2014

Timely topic as I'm adding a battery and winch to my trailer.

I'm pretty sure my '73 doesn't have the charge wire in the plug, as I had to add the trailer harness and brake controller... But it does have the isolator and relay under the hood for the second "camper" battery.

jimpaget · Mar 8, 2014

ChopTop84 said:
Delete the break-a-way battery, and wire direct to your winch battery. Its a better battery anyway, and odds are good your break-a-way battery is toast, as they dont last long. You just dont know it yet.

Great idea!!

zukkev · Mar 10, 2014

Well? You get her all figured out?

jimpaget · Mar 10, 2014

I got it figured out, but I haven't assembled the parts yet. Still unsure of what I am going to do for a battery box on the trailer.

Spent yesterday into the late evening working on a variety of computer issues.

zukkev · Mar 10, 2014

Ah, ok.
If it helps ya, we can build a battery box off the frame somewhere, once the battery size is figured out. I'd try and go with something common like a group 34, which is a lowish profile, but carries good CCA/reserve for the winch needs. There are smaller-sized ones out there with lower CCA too if you choose, but the CCA rating won't be near as good...