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Old 01-01-2020, 05:54 PM   #1
scottz
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Ford trailer battery charge circuit

Just found out something interesting and thought I'd pass it on; might save someone some time.

I have a water transfer pump that I use to refill the fresh water tank when dry camping. I had it set up with alligator clips, but thought I would be clever and wire it to a 7 pole connector and plug it into the back of the truck instead of running cable all the way to the front.

Well, Ford outsmarted me. When I turn the pump on, it runs for about two seconds then the voltage cuts off and the truck displays a message "Trailer Battery Not Charging". Not sure why; probably not worth messing with. I'm back to alligator clips now.
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Old 01-01-2020, 06:00 PM   #2
rohrmann
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That is strange. I have set up my pump with the plug and it works great. Not a Ford though.
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Old 01-01-2020, 06:17 PM   #3
Carl n Susan
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Yup Scott, the engineers screwed up using the Trailer Charge Line around 2017 (when the aluminum body came out). We were in Tucson with a member and his brand new Ford. He has a 12V water pump to fill/empty his water bladder when boondocking. He had used for a long tinm with a Bargman plug and his earlier Ford. But it didn't work with his 2017.

After several trips to a dealer (who has no idea), lots of volt meter readings and a query to the Ford Mother Ship, we learned the circuit doesn't really energize until afer the first use of the brakes.

I wrote a long post here about our adventure. I am damned if I can find it. The Search engines here are frustrating. But I will find it and when I do, I will link to it.

The answer to us was to use the Taillight Circuit connection (rather than the RV Charge circuit) in the RV plug. Of course you need to turn on the parking lights to energize the circuit.
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Old 01-01-2020, 06:22 PM   #4
Carl n Susan
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Ah ha I found the Post

http://www.montanaowners.com/forums/....php?p=1142356

As Gary subsequently learned, the 2017's and up no longer use the 12V charge line relay and circuit breaker. Their positions in the fuse panels have no circuitry to connect to. After several trips to the dealer, they finally learned about the new improved system.

All 2017 F-Super Duty vehicles equipped with a factory trailer brake controller (TBC) utilize a trailer module (TRM) which initiates the trailer charging system. For trailer charging to operate, the TRM must detect a trailer is connected and a brake pedal input before charging will be present at the trailer connector. Adding the trailer battery charge relay and fuse into the battery junction box are not required to operate trailer charging with a TRM. This is covered in Ford document SSM 46257.

Ref: https://www.etrailer.com/question-278872.html plus many other internet sources.
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Old 01-01-2020, 06:44 PM   #5
scottz
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Thanks. That sums it up well. I knew the brake pedal had to be pushed to activate it. I guess "not detecting a trailer" explains why it cuts off. The light circuit is the solution; if I can get motivated again.
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Old 01-01-2020, 10:46 PM   #6
Mr Pachu
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I'm just wondering if this would work? You connect the trailer cord to the plug in the box so that your truck recognizes that a trailer is connected and then you plug your pump into the bumper plug? Any thoughts about this? Or will the truck only supply power to one plug at a time?
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Old 01-02-2020, 12:28 AM   #7
scottz
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Quote:
Originally Posted by Mr Pachu View Post
I'm just wondering if this would work? You connect the trailer cord to the plug in the box so that your truck recognizes that a trailer is connected and then you plug your pump into the bumper plug? Any thoughts about this? Or will the truck only supply power to one plug at a time?
Who knows? But, when I'm filling my water tank, the back of the truck is near the back of the trailer not near the trailer cord.
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Old 01-08-2020, 03:50 PM   #8
paulinbaja
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I have a spare battery in a battery box in my truck bed. I plug this battery in whenever the fiver is not being towed. The reason is when boon docking it gets a full charge when I go fishing or on any excursion. I plug it into the 7 wire in the bed and the trailer into the bumper when the truck it at the trailer, thus extending our stay time. This would alleviate the goofy Ford connection issue for the pump. If you did this you would be using the extra battery to run the pump.
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Old 01-08-2020, 06:06 PM   #9
boisesmith
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I wired in a cigarette receptacle and have a cigarette plug on my water pump instead of alligator clips.
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Old 01-09-2020, 09:03 AM   #10
Rebel702
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Why not use the outfitter switches? Don't most SDs come with them? Install any style connect you prefer into bed.
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Old 01-09-2020, 09:34 AM   #11
boisesmith
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The plug is wired to the trailer batteries right at the convenience center so I don't need my truck close if I have already unloaded my water cans.
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Old 01-09-2020, 10:27 PM   #12
Todd727
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It's simple to trick the system. Wire a small resistor, between the brake light circuit and ground in the trailer plug you are using to connect whatever accessory you have. For me, it's a temporary fuel transfer pump when moving diesel to equipment.


You can wire the resistor to be inside the trailer plug.



You have to start the truck and then hit the brake pedal. After that, it will think there is a trailer and activate the 12v circuit.
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