F-150 charging (or not) trailer batteries

[Adrian Farmer]

We have a 2020 F-150 and have been towing our new 21NE for about three weeks. I’m not convinced that the truck is sending a charge to the trailer batteries while on the road, and limited evidence suggests that it is not doing so. An RV tech tested the pertinent plug on the truck’s 7 pin plug and determined it was not powered. So, I checked the associated fuse and replaced it with a new one.

I have since learned that newer 150s do not power the pin till:a trailer is connected, and the truck has been put into gear for at least 3 seconds.


Can anyone verify this? How do you test-start truck, put in gear, then back into park and leave running while unplugging and testing the voltage on truck side?


Thanks for suggestions.

[JeffreyG]

1) Have a friend sit in the truck, in gear, foot on the brake. If you can't find a friend for this:

2) Chock the wheels of the truck and set the parking brake. Shift into drive.

3) Check for voltage at the correct pin. Alternately, ground the pin through a resistor so it is under load, and then check the pin.

I do not know anything about the Ford approach to charging so I cannot comment on that.

One other thing, first step is look at the vehicle side of the 7-pin and see if there is even a wire running to the charging pin.

[Bea]

In case you don't have one, a 7 pin connector tester like this https://www.amazon.com/Miady-Trailer...xpY2s9dHJ1ZQ== might be helpful. Helped us figure out a wiring issue on our previous TV. -Bea

[Brian B-P]

If you don't have solar panels, you don't need to get to the charge line of the 7-pin connector to check it: with the trailer connected and having started and driven the truck, stop and check the voltage anywhere in the trailer. If the voltage is over about 13 V, the truck must be providing charge, since the battery by itself won't be that high.

If you have a connected solar system, you can't usefully check voltage to determine what the truck is doing unless you disconnect a wire between the 7-pin connector and rest of the trailer, because you don't know if the source of voltage is the solar charger or the truck. In some specific trailers, the trailer's battery disconnect switch (or "use/store" switch) may be useful for this... but may not be.

[Brian B-P]

Originally Posted by JeffreyG

1) Have a friend sit in the truck, in gear, foot on the brake. If you can't find a friend for this:

2) Chock the wheels of the truck and set the parking brake. Shift into drive.

3) Check for voltage at the correct pin. Alternately, ground the pin through a resistor so it is under load, and then check the pin.

I do not know anything about the Ford approach to charging so I cannot comment on that..

The problem is that Ford may be looking for load on the trailer lighting circuits (presumably just the tail/running circuit) to indicate the presence of the trailer:

Originally Posted by Adrian Farmer

I have since learned that newer 150s do not power the pin till:a trailer is connected, and the truck has been put into gear for at least 3 seconds.

The tester won't likely provide enough load.

[Vermilye]

Originally Posted by Adrian Farmer

We have a 2020 F-150 and have been towing our new 21NE for about three weeks. I’m not convinced that the truck is sending a charge to the trailer batteries while on the road, and limited evidence suggests that it is not doing so. An RV tech tested the pertinent plug on the truck’s 7 pin plug and determined it was not powered. So, I checked the associated fuse and replaced it with a new one.

I have since learned that newer 150s do not power the pin till:a trailer is connected, and the truck has been put into gear for at least 3 seconds.


Can anyone verify this? How do you test-start truck, put in gear, then back into park and leave running while unplugging and testing the voltage on truck side?


Thanks for suggestions.

I can verify it for a 2018 F 150. I have to put the truck in gear, wait a bit, then neutral to get the trailer feed live. I have a 7 pin pigtail that has built in LEDs that work as indicators to check that the 7 pin connector is functioning as expected. You can purchase a 7 pin receptacle tester. The tester works with mt 2018...