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Old 07-06-2022, 07:37 AM   #1
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F150 charging battery while towing

I have a 2018 F150 and would like to have 12v+ going to the battery while driving. What do I have to do?
Dealership says plug is working but it doesn't provide any juice.
Check the fuse and it's okay

Going to a different dealership but thought I would ask.
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Old 07-06-2022, 07:45 AM   #2
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Pin #4 is 12 vdc for charging, pin #1 is ground. With a multi meter check if you have 12 vdc (or so) on pin #4. If you do then the truck is providing 12 vdc to the camper unless there is a wiring issue from the camper plug to the battery
Also keep in mind charging your batteries with the truck 7 pin connector is not the most efficient. It's better to use your converter or a battery charger.
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Old 07-06-2022, 07:51 AM   #3
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Some vehicles have a relay in the fuse block as well as the fuse. Also some vehicles only provide 12V on the Bargman connector when the ignition is on. The wire gauge used by the vehicle manufacturer is usually sufficient to keep a charged TT battery charged, but little more due to the resistance and length of the wire. If you need to charge the TT battery, you will most likely need to run a heavier gauge wire for the 12V pin.
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Old 07-06-2022, 08:05 AM   #4
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It also may not supply power it a trailer is not connected, measure the voltage at the trailer battery with and without the truck running. It should be noticeably higher with the truck running.
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Old 07-06-2022, 08:19 AM   #5
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Actually I connected the trailer, Started the truck, and put a meter at the battery on the tt and it didn't change. Vs when you do the same with a 250 it jumps to 14v.
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Old 07-06-2022, 08:29 AM   #6
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Check the glove box and behind/under the seats to see if you can find a bad with some parts, at least one being a relay.

I am not sure is they still ship these un-installed but they used to
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Old 07-06-2022, 08:29 AM   #7
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Ford "trailer battery charge" connection is relay protected. Ignition must be On to get power there. (Sorry if I missed this.) There's also a fuze (and that relay) which I believe is under the hood -- at least on my Expeditions which are pretty close to the F150.

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Old 07-06-2022, 08:33 AM   #8
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Quote:
Originally Posted by Lead dog View Post
Actually I connected the trailer, Started the truck, and put a meter at the battery on the tt and it didn't change. Vs when you do the same with a 250 it jumps to 14v.
If the charging power is making it to the trailer's battery with a different truck the issue lies with the F-150 from the 7-pin connector to truck's battery where the 12v power originates. No need to chase the issue in the trailer.

Check fuse/fusible links at battery on truck.

As others have said, the power may only be present when a trailer is connected and sensed by the body control module through a relay.

Maybe this simple video will help:

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Old 07-06-2022, 08:38 AM   #9
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Simple relay to the ignition controls Ford trailer battery charge. No exotic sensing circuitry. But the ignition has to be On. This is there to prevent the trailer from draining the truck battery when parked -- some if not most GM trucks lack the relay and will kill the truck quickly when parked if there are large 12v draws in the trailer -- need I mention 12v refrigerators?

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Old 07-06-2022, 04:22 PM   #10
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Quote:
Originally Posted by cboss View Post
Also keep in mind charging your batteries with the truck 7 pin connector is not the most efficient. It's better to use your converter or a battery charger.
Unless the OP has a generator onboard, it would be hard to use either to charge the battery while driving
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Old 07-06-2022, 04:46 PM   #11
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connect volt meter to battery on trailer should read :

12.6 volts not connected to truck or when truck connected but not running



closer to 14v when truck running.... depending on your alternator you may have to increase revs


if the battery reads the same 12.6
make sure it is not turned off (isolated)


make same measurements at the truck

without trailer connected if the red charging wire not increasing to 13+ volts something wrong in the truck wiring / relay
if it is increasing to 13+v then the problem is in the wiring to the battery on the trailer
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Old 07-06-2022, 05:19 PM   #12
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Daughter and son-in-law's new trailer with 12 volt only frig would kill the trailer battery between home and campground. They asked the dealer about it and he looked in the fuse block under the hood and there was no trailer charge relay (F150). He installed one and all works now.
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Old 07-06-2022, 05:25 PM   #13
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OP'er, did you by chance read the owners manual? It will have the answer for you but I suspect you will need a fuse and a relay. Good luck.
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Old 07-06-2022, 05:40 PM   #14
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Quote:
Originally Posted by llr View Post
Check the glove box and behind/under the seats to see if you can find a bad with some parts, at least one being a relay.

I am not sure is they still ship these un-installed but they used to
Our 2013 F150 had the needed parts packed away in the glove box. A techie at WanaRV told us to look there
or we would never have found the needed parts. Once installed, the battery charged while we towed the trailer.
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Old 07-06-2022, 06:58 PM   #15
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My 2019 f150 does not send power to the trailer auxiliary power Unless the truck is in gear. You may consider rechecking the voltage at pin 4 with truck in neutral or if in gear with someone holding the brake.
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Old 07-06-2022, 07:12 PM   #16
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Our 2019 F-150 appears to be charging the battery. After long drives battery shows full, even with the 12v fridge running. Haven't checked to see if it was only while in gear. Don't remember having to do anything to make it work.
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Old 07-06-2022, 08:25 PM   #17
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You didn't mention what trim level of F150 you have.

I have a '19 F150 Lariat which has a push button start. To get voltage here are the hoops needed.

Engine running, press brake pedal so the truck recognizes there is a trailer attached, leave the FOB inside the truck, fully close all doors on the truck. You'll see the 13.5V or so on the 12v pin. Skip any of the hoops listed above you'll have ZERO volts.

Hope this helps
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Old 07-06-2022, 09:24 PM   #18
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Quote:
Originally Posted by Mike134 View Post
You didn't mention what trim level of F150 you have.

I have a '19 F150 Lariat which has a push button start. To get voltage here are the hoops needed.

Engine running, press brake pedal so the truck recognizes there is a trailer attached, leave the FOB inside the truck, fully close all doors on the truck. You'll see the 13.5V or so on the 12v pin. Skip any of the hoops listed above you'll have ZERO volts.

Hope this helps
Interesting. Ours is the 2019 XLT without the pushbutton start. The display acknowledges there is a trailer connected the moment you plug it in or if it is already plugged in when the truck is turned on. Now you got me wondering. it seems like our battery has been charging fine on several long trips. i suppose I will recheck the manual as well.
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Old 07-07-2022, 09:11 AM   #19
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Dc to DC Charger

You might want to check out a dc to dc charger.
Check this:
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Old 07-11-2022, 08:55 PM   #20
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I have a 2018 F150. Turn the lights from auto to on.

Forgot need truck running.
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