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Old 09-19-2020, 04:50 PM   #1
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Seven pin trailer connector 12vdc power

I realized that my rv trailer batteries are not charging from my tow vehicle. I looked up the wiring and found the 12vdc power terminal is at about one o'clock, and the ground is at about seven o'clock on the truck. With the truck running I do not get any power between the 12vdc terminal and ground. I'm figuring I should have power at this time. I checked my fuses and they check out as being good. I also pulled the plug from under the truck and checked those terminals, and get the same results. All the trailer lights and brake work perfectly.

Any ideas on where to go from here???
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Old 09-19-2020, 05:09 PM   #2
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Open up the trailer plug and see if you have any wire off the 12vdc hot. (4)
Probably the trailer wasn't wired for it.
Lights, brakes are all seperate fromthe 12 volt for charging.

Here is the 7 pin layout for a typical trailer.
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Old 09-19-2020, 06:56 PM   #3
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I used a similar chart to find which terminal was hot.....but it's not....no voltage....
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Old 09-19-2020, 07:18 PM   #4
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If your truck is a Ford please let us know.

Include if it's a pushbutton start, there are several hoops you must jump though get power at that 12V terminal.
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Old 09-19-2020, 07:31 PM   #5
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If your truck is a Ford please let us know.

Include if it's a pushbutton start, there are several hoops you must jump though get power at that 12V terminal.
Yea, it's always helpful if posted year, make and model of truck and trailer, since you don't have any of that information in your profile.
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Old 09-19-2020, 07:39 PM   #6
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I have a new F350 - interested in hearing about this.
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Old 09-19-2020, 07:39 PM   #7
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Yes...sorry...you're absolutely right. 2014 Ram 4x4 1500. I'm not sure when it quit working as we drove it to Alaska pulling a trailer a couple years ago and it worked fine then...then traded in the trailer on a motorhome and I didn't tow during that time. This year, we are towing a new trailer, but until last week always had ac power on site. This week we did some dry camping and found the batteries weren't charging betwen sites at all....
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Old 09-19-2020, 07:59 PM   #8
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Sorry can't offer any help for a Ram.


The Ford 12V charge line doesn't work unless you have a trailer connected, truck running, press the brake pedal for about 3 seconds and have all the doors fully closed. And if it's a push button start leave the fob inside the running truck.
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Old 09-19-2020, 08:04 PM   #9
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Thanks Mike - appreciate the info.
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Old 09-19-2020, 08:11 PM   #10
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Yes...sorry...you're absolutely right. 2014 Ram 4x4 1500. I'm not sure when it quit working as we drove it to Alaska pulling a trailer a couple years ago and it worked fine then...then traded in the trailer on a motorhome and I didn't tow during that time. This year, we are towing a new trailer, but until last week always had ac power on site. This week we did some dry camping and found the batteries weren't charging betwen sites at all....
Your Ram, if operating correctly, will only provide a trickle charge at best while driving. So if the battery was discharged before moving to another dry camp spot, unless you drove 8-12 hours, the battery was probably never fully recharged.
You should have the battery fully recharged and then load tested or hydrometer tested.
Then deal with why your truck is not providing power through the charge wire.
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Old 09-19-2020, 08:44 PM   #11
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Thanks..I will check with a better voltmter when I get home....
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Old 09-20-2020, 03:39 PM   #12
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For Chevy Owners:

FYI for Chevy owners: Some of the Chevys, even the ones with towing packages do not come with pin 4 connected (12V Aux). You need to go under the hood and find the lead with the loop connector buried in the wiring harness next to your fuse box. Remove the lead and connect it to one of the external hot terminals using your own nut (remove fuse box cover to expose your hot leads).



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Old 09-20-2020, 03:49 PM   #13
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Originally Posted by chengdave View Post
Yes...sorry...you're absolutely right. 2014 Ram 4x4 1500. I'm not sure when it quit working as we drove it to Alaska pulling a trailer a couple years ago and it worked fine then...then traded in the trailer on a motorhome and I didn't tow during that time. This year, we are towing a new trailer, but until last week always had ac power on site. This week we did some dry camping and found the batteries weren't charging betwen sites at all....
On your Ram the trailer tow fuses are F28, F29 & F30 in the underhood fuse box. F30 is a mini fuse. Be sure to test all those.
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Old 09-20-2020, 04:44 PM   #14
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Thank you! I'll have another looksee!!!
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On your Ram the trailer tow fuses are F28, F29 & F30 in the underhood fuse box. F30 is a mini fuse. Be sure to test all those.
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Old 09-21-2020, 05:05 AM   #15
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I didn't find out for over 7 or 8 years that my 2008 2500 GMC Sierra D/A wasn't charging either. My trailer repair guy fixed the issue right away as he knew exactly what to do.
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Old 09-21-2020, 05:24 AM   #16
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I didn't find out for over 7 or 8 years that my 2008 2500 GMC Sierra D/A wasn't charging either. My trailer repair guy fixed the issue right away as he knew exactly what to do.
It would be more helpful if you could tell us what he did to fix the problem.
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Old 09-21-2020, 10:10 PM   #17
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It would be more helpful if you could tell us what he did to fix the problem.



See my post above. Chevy, GM are the same.
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Old 09-21-2020, 10:18 PM   #18
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See my post above. Chevy, GM are the same.
You mean "Chevy, GMC", right? Are you sure that's what Splashes3's repair guy did or was there another issue?
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Old 09-21-2020, 10:55 PM   #19
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You mean "Chevy, GMC", right? Are you sure that's what Splashes3's repair guy did or was there another issue?

Current GM auto brands are Buick,Cadillac, Chevrolet, GMC, Holden and Wuling. Former GM automotive brands include La Salle, McLaughlin, Oakland, Oldsmobile, Opel, Pontiac, Hummer, Saab, Saturn and Vauxhall and Daewoo.



99% sure. They don't come hooked up and if you don't test pin 4, you'll never realize it. I'm actually considering putting a switch on mine. So when I'm not "trailering" there's less chance of shorts should the 7 pin outlet get wet.



BTW: If you use a wireless brake controller, pin 4 is what powers it.
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Old 09-23-2020, 11:05 AM   #20
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I checked my voltage with a good multimeter (Fluke 77) when I got home. I'm getting 4vdc without a load on the 12vdc terminal of my 7 blade truck trailer connector. I thought charging rate was according to amperage, not voltage. But then I never claimed to be an electrician.

What say ye???

PS: I did check my fuses, and all tested good. There's actually five fuses....including F53 and F81.
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