baffled by 12v issue

[f100owner]

Be aware, on Fords (at least on the newer F series), 12v is not delivered to the 7 pin UNLESS the vehicle is in gear. I had an issue with a 2019 F-150 not powering the electric brakes. Tech checked it, replaced the plug, same issue. When he checked the data base to see if there could be another issue, he found the info about the vehicle being in gear. (He is an electrical/electronic specialists and honestly forgot.). Put the truck in gear and all pins powered. Turned out to be trailer brake control was defective. Anyway, traded in 150 for 2020 F-250 and that issue went away and we have a much more comfortable ride and power. WIN WIN!!!!

Had no heard or read about the truck needing to be in gear to power, I assume only applies to the black/charging circuit.
My move to the 2021 F250 fx4 7.3L crew was a win from a towing perspective - had to make the move before we switched to the 3250BH from the 2800BH. From a ride and enjoyment perspective I miss my 2020 F150 with V8. Even with upgraded shocks on the f250, while the ride improved a lot, the f150 with its Roadmaster Active Suspension system and upgraded shocks was my most enjoyable pickup to date to drive (and I have had a few starting in the 10th grade with a 72 F100 Ranger XLT).

[Dan and Deb]

Keep in mind this is just tossing out possibilities without hands on.

Hooking the trailer to the truck could cause this if the 12vdc wire which comes from the truck is grounded somewhere so that it is giving ground instead of 12VDC..

The more likely culprit would be the cord on the trailer with the plug that goes to the truck. If there were a pinched or bare spot in that cable it could be getting grounded inside that cable and that ground could be coming and going based on the cable position.

I would not suspect a problem on one of the 12volt circuits inside the trailer such as the lights or exhaust fans as my first choice because those circuits are protected by fuses that are much lower rated than the breaker. Those fuses SHOULD blow before there is enough current draw to trip the breaker, if the breaker is working properly, so the problem most likely lies before the 12vdc fuse panel.

A grounded wire in the truck harness would cause a blown fuse in the truck before ever connecting to the trailer. I agree that the issue is must likely before the trailer wire reaches the converter. A couple other possibilities are a short inside the converter or a defective breaker/fuse tripping too easily

[more tired since retired]

Had no heard or read about the truck needing to be in gear to power, I assume only applies to the black/charging circuit.
My move to the 2021 F250 fx4 7.3L crew was a win from a towing perspective - had to make the move before we switched to the 3250BH from the 2800BH. From a ride and enjoyment perspective I miss my 2020 F150 with V8. Even with upgraded shocks on the f250, while the ride improved a lot, the f150 with its Roadmaster Active Suspension system and upgraded shocks was my most enjoyable pickup to date to drive (and I have had a few starting in the 10th grade with a 72 F100 Ranger XLT).

You are correct, the truck will not provide power to the charging circuit unless the truck is in gear.

When the tech realized that and he saw power at the 7 pin, we hooked the F-150 to another trailer and had the same issue. We brought the truck in with our trailer hooked up. That was what led to pulling the brake controller and replacing it. Problem solved and Ford wanted the controller back. Their testing said the switch was bad, apparently a cold solder joint inside the switch.

And I agree, the 250 is a win from the towing perspective. Only issue it is my everyday driver and MPG in town sucks (figuratively and monetarily). Towing went from about 8 MPH with the 2019 F-150 5.0L to about 14 MPG with the 6.7L (includes a lot of mountain driving).

[f100owner]

A grounded wire in the truck harness would cause a blown fuse in the truck before ever connecting to the trailer. I agree that the issue is must likely before the trailer wire reaches the converter. A couple other possibilities are a short inside the converter or a defective breaker/fuse tripping too easily

Going to look at the wiring harness on the trailer side some.
Would also like to identify what each of the wires going to the breaker does. Seems like a lot of wires going into the breaker. A coworker told my his son's travel trailer has three of this style of breaker on it.
Referencing the towing with the f250 vs f150. I did not go diesel route. Only tow once a month for 9 months and the rest of the time the truck is either my daily or sits in storage while I drive something else. My 7.3L gets about the same MPG (8) towing the 3250 as my previous two f150s (one a 2.7 and the other a V8) along with our Expedition all got between 6 and 8 towing the 2800BH we had previously.

[LMagelitz]

Going to look at the wiring harness on the trailer side some.
Would also like to identify what each of the wires going to the breaker does. Seems like a lot of wires going into the breaker. A coworker told my his son's travel trailer has three of this style of breaker on it.
Referencing the towing with the f250 vs f150. I did not go diesel route. Only tow once a month for 9 months and the rest of the time the truck is either my daily or sits in storage while I drive something else. My 7.3L gets about the same MPG (8) towing the 3250 as my previous two f150s (one a 2.7 and the other a V8) along with our Expedition all got between 6 and 8 towing the 2800BH we had previously.

I’d check to make sure the charge wire coming from the truck is fused where it connects to the trailer’s 12v system. If it’s not (mine wasn’t), your trailer batt(s) will feed any fault that might occur in the cord back to the truck until something burns up.

[traveldawg]

Going to look at the wiring harness on the trailer side some.
Would also like to identify what each of the wires going to the breaker does. Seems like a lot of wires going into the breaker. A coworker told my his son's travel trailer has three of this style of breaker on it.
Referencing the towing with the f250 vs f150. I did not go diesel route. Only tow once a month for 9 months and the rest of the time the truck is either my daily or sits in storage while I drive something else. My 7.3L gets about the same MPG (8) towing the 3250 as my previous two f150s (one a 2.7 and the other a V8) along with our Expedition all got between 6 and 8 towing the 2800BH we had previously.

That looks like a lot of wires feeding off of just one breaker. This might not be to your liking, but to isolate the problem I would suggest running each of those wires (it looks like 4; 5 if you count one connection with 2 wires) on it's own manual resetting breaker. Hopefully only one breaker will trip and you can chase down that single circuit.