Power from truck through 7-pin harness?

JohnMD · 04-10-2023, 08:24 AM

Hi all,

We just returned from our first trip of the season. On the trip, I discovered that I am not getting any power or battery charging through the positive pin on the 7-pin connector. Using a multimeter, I checked the other pins and everything else seems to work. I held the negative pin of the multimeter to the ground pin on the Bargman (truck side) and moved the positive pin to each of the other connectors, engaging lights, etc.. All lights and brake controller are getting power, but 0 volts when I connect my multimeter to the positive/aux pin. I tried cleaning the contact, but no success. Any thoughts or suggestions?

John

Shane826 · 04-10-2023, 08:30 AM

What’s the tow vehicle? A lot of vehicles need a fuse installed or a cable attached to the fuse block in order to send power back to the 7-pin connector.

JohnMD · 04-10-2023, 08:35 AM

Shane,

2017 F150 3.5 Eco Boost.

I looked at the fuse chart in the manual and saw a few labeled for tow lights, but nothing that looked applicable to 12v power to trailer.

Thanks.

Shane826 · 04-10-2023, 09:02 AM

Ah. According to the online owners manual, the truck has to “see” that there is a trailer attached before it will send power to the 12V+ pin. I guess you could jump both brake/turn pins to ground, turn the truck on, and hold the brakes for a few seconds… That might trick the truck into thinking a trailer is connected? Then you could check for 12V+.

This gets a lot easier with a scan tool. Stupid smart vehicles. They think they are so smart. But they’re not. They are STUPID.

PS- How did you come to the conclusion that the trailer isn’t getting power from the truck? Here’s an easier test… Disconnect the trailer battery, solar, etc and unplug from shore power. Plug the trailer into the truck and make it “recognize” the trailer. Turn on some lights inside the trailer (not towing lights). Do they work? Your truck is sending power to the trailer…

**Bill** · 04-10-2023, 09:12 AM

I'm thinking Shane is right - the computer has to recognize that there is a trailer attached. On my 2014 F-150, this is easy to check. There is a 4-way rocker switch on the left end of the steering wheel spoke. Moving this rocker changes what is displayed on the front panel display. If I go to a display called Truck Apps, and maybe toggle back and forth a couple times, it will say either "No Trailer" or "Standard Trailer Connected" or "Trailer Disconnected". As Shane says, it must tell you that the trailer is connected. The truck "detects" that a trailer is connected by looking at the electric brake line, rather than the brake lights. In other words, it won't send power to a light-weight utility trailer that doesn't have electric brakes, and so does not have a battery. This means, of course, that when you pull the 7-pin connector, the trailer brakes are no longer sensed, so power to the battery charge line is turned off.

If that is not the issue, was your 7-pin connector OEM or after-market? Again on my truck (OEM installation), there are two fuse boxes. One is under the hood above the radiator. The other is inside, in the passenger foot well. When we picked up the truck from the dealer, the components for the 7-pin trailer connector were in a plastic bag in the glove compartment.

For the inside fuse panel, the diagram identifies two components that are involved. There is a relay (component #9) and a 30-amp cartridge fuse (component #21). If either of these is missing, there will be no power at the connector, of course.

On the 2017, I think the under-hood fuse box is on the right, near the battery. The inside panel is on the right, on the wall of the passenger foot well. I have no idea how close the individual fuse locations in the 2014 panels match the 2017 panels.

Bill

JohnMD · 04-10-2023, 09:26 AM

Shane and Bill,

Thanks for the feedback. During our trip, I decided to plug into the truck to see how quickly the battery would charge while idling for a few minutes. This wasn't necessary as I had my generator, but I was just curious. My battery showed no voltage change when connected to truck with engine on. Prior to leaving the campsite, my battery read at 12.4 volts. After the three hour trip home, it still read at 12.4 volts.

I also read about how the truck needs to recognize the trailer in order to supply 12v power. In the meantime, I cleaned the trailer's Bargman connector again with terminal cleaner and used Bill's cardboard trick and the truck now sends power to the trailer and everything seems fine. Go figure. I guess the connections needed to be a little cleaner.

John

jgilliam1955 · 04-18-2023, 12:24 PM

In my Colorado, I have to push the trailer button and have to turn on the headlights to get my battery to charge, pulling the trailer. If I forget the lights the truck battery will start losing volts over time. Thanks for your information.

EZCAMPER · 04-19-2023, 08:08 AM

Quote:

Originally Posted by JohnMD

Hi all,

We just returned from our first trip of the season. On the trip, I discovered that I am not getting any power or battery charging through the positive pin on the 7-pin connector. Using a multimeter, I checked the other pins and everything else seems to work. I held the negative pin of the multimeter to the ground pin on the Bargman (truck side) and moved the positive pin to each of the other connectors, engaging lights, etc.. All lights and brake controller are getting power, but 0 volts when I connect my multimeter to the positive/aux pin. I tried cleaning the contact, but no success. Any thoughts or suggestions?

John

John, when I had Uhaul add my 7 pin harness, I found that that pin is not always connected. On some vehicles, there is no access in the rear. In that case, they would have to run a wire from the front. They usually connect a separately fused wire to the battery and snake it back. There is usually an up-charge for that. Luckily, I had an accessible wire at the back, so they automatically connected it.

**Bill** · 04-19-2023, 09:42 AM

EZCamper -

Good to know. Thanks.

If you snake a new wire from the front, make sure it is at least 10-gauge. Bigger wouldn't be a bad idea, but it might be hard to insert it into the connector at the bumper. Do your best to make sure it is a single piece of wire, without junctions or splices.

Bill

JohnMD · 04-19-2023, 06:04 PM

This is interesting and appreciated information. As I wrote in my follow-up, after cleaning the connections on the trailer side again, using Bill's cardboard suggestion, everything seems to be working again now.

Thanks again,

John