7-Way Trailer Connector Not Charging Battery

[Chris McN]

We took our new '21 F-150/Airstream combo on its maiden voyage this week. I realize that the 12 volts offered thru the 7-way trailer connector gives little more than a trickle charge but when we got to our destination I was surprised to see that it hadn't charged the trailer batteries at all. I put a multimeter to the 1 o'clock and 7 'o'clock pins in the truck-side connector expecting a 12V reading but got nothing. I checked with the truck turned off, in accessory mode and with the engine running.

I read that in prior gen F-150s Ford left it to the buyer to install a relay to enable trailer battery charging but I can't find any info on this in any of the 2021 documentation.

Any thoughts on this? Thanks in advance.

Sponsored

 

[Chris McN]

Bumping.......

 

[daemonic3]

Hmm. I had a 2017 Ecoboost and was stranded with my trailer at a truck stop overnight. The trailer obviously can run most of the controls off the 12V batt but not meant for long term without recharging. I noticed that my trailer batt meter said "low" the next morning. I still had it attached and the 7-pin connected, so I ran the truck engine for about 15 minutes. The trailer battery said "full" now.

So at least in my anecdotal evidence, the 7-pin seemed to carry enough charge to replenish my battery. I didn't probe the voltages at the connector though.

I have never heard of this relay you mention.

 

[Geo]

We took our new '21 F-150/Airstream combo on its maiden voyage this week. I realize that the 12 volts offered thru the 7-way trailer connector gives little more than a trickle charge but when we got to our destination I was surprised to see that it hadn't charged the trailer batteries at all. I put a multimeter to the 1 o'clock and 7 'o'clock pins in the truck-side connector expecting a 12V reading but got nothing. I checked with the truck turned off, in accessory mode and with the engine running.

I read that in prior gen F-150s Ford left it to the buyer to install a relay to enable trailer battery charging but I can't find any info on this in any of the 2021 documentation.

Any thoughts on this? Thanks in advance.

Did you ever get your problem solved. I am having the same problem No 12 volt power from plug to trailer. and no trailer brake.

 

[LHoffmanjr22]

Did you ever get your problem solved. I am having the same problem No 12 volt power from plug to trailer. and no trailer brake.

I don't know about the trailer brake, but I did a little research on charging a trailer battery, and found that in the fuse box of the truck, Fuse # 107 is needed in order to enable the charging capability. I have yet to check on my own truck if it is actually there or not, but I would imagine that if it's not there you'd just need to put a 30 amp fuse into slot 107 and it would start charging. I haven't tried anything yet, but just a though if someone has time to look before I get around to it.

 

[Geo]

I don't know about the trailer brake, but I did a little research on charging a trailer battery, and found that in the fuse box of the truck, Fuse # 107 is needed in order to enable the charging capability. I have yet to check on my own truck if it is actually there or not, but I would imagine that if it's not there you'd just need to put a 30 amp fuse into slot 107 and it would start charging. I haven't tried anything yet, but just a though if someone has time to look before I get around to it.

Yes, I checked #107 trailer tow battery charge 30 amp. Also checked #42 trailer brake control module 30 amp. Pulled and checked both, they were OK. If and when I get it fixed I'll let you know. Thanks for the reply.

 

[Chris McN]

Did you ever get your problem solved. I am having the same problem No 12 volt power from plug to trailer. and no trailer brake.

I read somewhere on another forum that the new generation F-150s only energize the 7-way charging pin if a trailer is detected. That would explain the lack of a voltage reading. I don't know if that true or not since there's no simple way to measure it if the trailer is connected.

The fuse/relay explanation seems unlikely to me as you would think (hope) that Ford would state this in the manual somewhere.

 

[Niterider]

I read somewhere on another forum that the new generation F-150s only energize the 7-way charging pin if a trailer is detected. That would explain the lack of a voltage reading. I don't know if that true or not since there's no simple way to measure it if the trailer is connected.

The fuse/relay explanation seems unlikely to me as you would think (hope) that Ford would state this in the manual somewhere.

My 2014 F-150 wouldn't send power to the plug if it didn't detect a trailer. Something about it if it doesn't detect brakes, then it doesn't think there is a trailer there. If I remember right, I had to change a setting in the dash to force it to acknowledge the trailer I was pulling. (homemade fuel trailer that uses 12v to pump the fuel)

 

[Geo]

My 2014 F-150 wouldn't send power to the plug if it didn't detect a trailer. Something about it if it doesn't detect brakes, then it doesn't think there is a trailer there. If I remember right, I had to change a setting in the dash to force it to acknowledge the trailer I was pulling. (homemade fuel trailer that uses 12v to pump the fuel)

Yes these new trucks are pretty smart. After paying close to 2k for max tow I would think it would be ready to go. My RV is at a storage site down the road. When the rain lets up in a day or two I will go over and dig a little deeper. In the past I have always stored my RV with the battery's removed. When doing so I would have to cover or tape off the positive lead wire to the RV battery's. If the positive and negative wires to the RV battery made contact with each other, then it would blow a fuse in my truck. So that tells me there is voltage going to the positive lead all the time weather there is a battery there or not. We'll keep digging.

 

[Wife of unhappy hubby]

Has anyone found a fix to the battery not charging? Unfortunately, we are on the road and came across this issue.

 

[Niterider]

Has anyone found a fix to the battery not charging? Unfortunately, we are on the road and came across this issue.

Did you check to see if you have the relay installed for trailer power? I can’t say if the current trucks now include that relay, but I haven’t seen a truck yet with one from the factory.

If you are on the road and in a pinch, you could use the relay from from the rear window defroster. That’s what I did with my truck. I never really used the rear defrost much anyway.

 

[Hawkeye]

Did you check to see if you have the relay installed for trailer power? I can’t say if the current trucks now include that relay, but I haven’t seen a truck yet with one from the factory.

If you are on the road and in a pinch, you could use the relay from from the rear window defroster. That’s what I did with my truck. I never really used the rear defrost much anyway.

I don't see a relay for it in either the under hood fuse box or the smaller one in the cab. My STX w/tow tech has fuses in the correct location.

If your trailer has LED lights there might be an issue where there isn't enough load on the smart trailer system and you'd have to tell it you have a trailer hooked up for the 12v to work.

 

[Niterider]

If your trailer has LED lights there might be an issue where there isn't enough load on the smart trailer system and you'd have to tell it you have a trailer hooked up for the 12v to work.

I thought I read somewhere that the trailer detection was based on trailer brakes....

And well...after looking at the online user manual for 2021 trucks...maybe they did away with a lot of the relays? Either that...or this online manual is really thin on info.

*If* I do get my truck this week (ETA is 5/12) then I'll probably spend some time with it out on the farm with my multi-tester to see if the power output on the plug is working. We have a 300 gallon fuel tank that we can pull around and it uses the power from the truck's plug to run the fuel pump.

 

[defran02]

Doing a cross country trip an realized we don't have 12v power on the 7 pin harness either. Truck recognizes a trailer is attached, but no power. Fuse 107 is in place and is good. Also have had the alarm go off serval times when a trailer is attached and we lock the truck. The truck says the trailer was disconnected when it was not. And of course it happens at night.

Also it has happened on two different trailers, so it is not the trailers.....

 

[kdkool]

I don't have a Gen14 yet, but on my 2015, the trailer 7-pin cable only energizes the 12V pin after a trailer has been detected and is put into drive or reverse for three seconds. It will stay energized even if you put it in back into park but will turn off as soon as the trailer cable is disconnected. If you just measure the output without a trailer connected, you'll never get a reading.

Sponsored