Wiring battery on trailer to charge--part 2

DRL · Jul 8, 2009

Been binding wheat the last couple of days, so didn't get a chance to look and all your answers until today. I appreciate everyone's input.

My tow vehicle is an '04 Ford F350 with the factory tow package. Some of you said that your Ford of around the same vintage had a trailer battery charge circuit already installed. The website that Old Roy was kind enough to share shows that the #4, black terminal is the battery charge circuit on a 7 pin connector. Some of you said you use the center aux. terminal. Which one is the best to use, and would I need the batt. isolator when using either one of these pins, or does the tow vehicle wiring circuit do that for you? Also, if using the factory charge circuit, is an additional circuit breaker or fuse necessary? Thanks again.
Original Discussion

504-2 · Jul 8, 2009

To answer most of your questions I would ask and tip 5.00 to the mechanic at your local RV dealer. The chart I have says to use #4 pin for charge and that #7(center) is most often used for back up lights.(which I am thinking would be an excellent addition to my trailer) 20ft trailer, 3ft tongue, 8ft truck bed and 3ft extend cab,that is a long way after dark! It does make me feel better after adding up the length that I can not see in the dark any more the back the thing!

fixerupper · Jul 8, 2009

So you don't want to go bump in the dark? I just had to say that!LOL

Yes, I've seen wiring diagrams that suggest the middle terminal be used for backup lights.

Backup lights would be nice on semi-trailers too. I often drag the brakes while backing up in the dark so the brake lights illuminate the object just before I hit it.Jim

Old Roy · Jul 8, 2009

I believe what you are referring to as a battery isolator is in most diesel equipped trucks that have two batteries under the hood . one for starting and the other for lighting system.

a trailer that would be often taken off tow vehicle would only charge when traveling when you unplugged the connection between the tow vehicle and trailer it would be isolated.

Starting the tow vehicle wouldn't have much effect on the winch battery, at least not enough to worry about.

The wiring diagram is good for any trailer that has that same plug and if you hooked up backup lights even if you picked up one that didn't hav B/U lights it would still work without a problem.

You can even get a 4 wire Flat plug adapter for like a boat trailer, or utility trailer and your same plug will work.

KEB1 · Jul 8, 2009

First off, diesel pickups simply run two batteries in parallel to give more starting capacity...electrically its exactly the same as one battery with twice the capacity.

The trailer charge line normally goes to pin # 4. Simple to check, it should be hot when the engine is running and not when you shut the key off. None of the other lines are hot except when a light or the brakes is active.

The factory charging circuit should have a fuse installed. On my '99, its one of the large fuses under the hood. Look at the list of fuses in the manual, it'll list one for charging a trailer battery, or some similar term.

Here's another link to a site showing the "standard" connections. I checked my travel trailer, & sure enough the battery charge circuit is on pin 4, not on the aux terminal. If you're not going to use your trailer on another vehicle, or tow someone else's trailer, it really doesn't matter.

Keith
Bargman connector wiring

John M · Jul 9, 2009

Look on the cover for the connector on the truck. Its on there.

Wiring battery on trailer to charge--part 2

DRL

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504-2

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fixerupper

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Old Roy

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KEB1

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John M

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