GEN 2 Trailer interior lights

[sfckelley]

Quick question, I have a 7x14 trailer hooked up to my 18 with the pro trailer package or whatever it is called. All the exterior lights work but the interior lights will not come on. Truck running, headlights are on and nothing. I checked the trailer with another truck and they work fine. I recall my previous f150s needing a relay installed, but do not see one in the glove box nor a mention of it in the manual. Anybody know what I’m missing??


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[sigocentral]

Maybe try turning on the truck's interior lights using the button next to the headlight ring knob? it's on the dash to the left of the steering wheel. Also, check your electrical pins in the connector and clean them if dirty.
best of luck!

 

[sfckelley]

Thanks, tried that with no luck. Get this, when I press the brake pedal, the lights come on! Crazy that they will only work when the brake pedal is depressed.


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[xxaarraa]

Very interesting. I have a 7x14 that I tow with the Raptor all the time and I did not know about this. Does this mean that when the brakes are depressed, the 7 pin connector provides power to the trailer???

I have a Group 31 house battery in my trailer that powers all interior lights / fans / fridge etc. so never looked into whether truck will provide power to trailer. However, it would be nice to find a way for truck to charge the onboard house battery while towing!

 

[sfckelley]

I have been researching this anywhere I can, I read over on the F150 forum that the trailer battery charge pin only supplies enough power to "trickle" charge a battery (maybe by only supplying 12 volts when the brake pedal is pressed). I can't understand why Ford decided to do it that way.

 

[Jr24]

That's strange. I would say there is a strange grounding issue in the trailer or there is a wiring issue in the trailer circuit on the truck that has been possibly been there since new, but wasn't apparent until you hooked up a trailer. I have both a 6' X 14' foot utility trailer and a boat trailer that I have pulled with my 2018 802a and have had no issues with either the lights on my trailers or the interior lights on my truck.

Have you by any chance tried a different trailer to see if the issue persists? That might be the first thing I would do. Also, if you are using any kind of plug-in adapter between the trailer and truck plug, I have seen adapters go bad or have internal shorts which wreak havoc and cause strange issues with different lights.

 

[ChevyChad]

OP- I have your same problem! My trailer has interior lights that use power from the truck but do not come on at all. I have not tried pressing the brake in the truck to see if that makes them come on. But I agree, this is BS that the interior trailer lights do not work as they should unless the brake on the truck is depressed if that is the case!

 

[BigCSS78]

Most of the time the factory doesn’t have the fus in the spot for the 12 volt charging circuit on the trailer plug. So I would check the fuse box under the hood and you may need to install that fuse. I know my ‘07 gmc was that way and I can’t remember if it was that way on my ‘11 F-450.
Edit: after a little googling it only has power when the vehicle is running. So try it that way and see.

 

[sfckelley]

Thanks for the help and advice everyone. I read the owners manual thoroughly and contacted Ford about this. There is no fuse or relay that needs to be added to our trucks. Once the plug is connected, the truck should recognize the trailer and send power where it is needed. I have an appointment with the dealer on Friday (with very low expectations) and will report back on the outcome. To clarify, this issue is not with the truck's interior lights, it is with the trailer's interior lights. I have tried with the truck running, lights on, parking lights on, lights off, and just about every other conceivable configuration. I read over on another forum that the truck needs to be off prior to connecting the plug and then the brakes held for 3-5 seconds when started in order for the truck to recognize and send power, so I tried that last night and still nothing!

 

[Loufish]

The charging circuit which would run your lights is only on when the truck is running, otherwise you could leave something on and kill the trucks battery...old school trucks did have constant power...

 

[sfckelley]

Just returned from my dealer visit to get this resolved. They have no answers, had to email Ford themselves for further guidance. They are not getting power to the pin for the interior trailer lights either though, so at least it's not just me missing something easy.

 

[jzweedyk]

I have seen a million dollar Motor Home where they wired the trailer plug wrong. If you are not getting power at the plug, check the wiring.

 

[sfckelley]

I just read that the doors have to be closed, truck running, key fob inside the truck in order for the 12v to be live. This includes the interior lights. Will be checking tonight.


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[TXRaptor]

I just read that the doors have to be closed, truck running, key fob inside the truck in order for the 12v to be live. This includes the interior lights. Will be checking tonight.

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That seems like a very narrow use case of the 12V to a trailer. If you are in the truck with it running, why would you need the interior lights to be on inside the trailer? Someone at Ford did not think it through, as interior lights on a trailer are fairly common and you need them on when you are NOT in the truck and when it is NOT running!

I guess they are trying to save us from ourselves...

 

[Loufish]

That seems like a very narrow use case of the 12V to a trailer. If you are in the truck with it running, why would you need the interior lights to be on inside the trailer? Someone at Ford did not think it through, as interior lights on a trailer are fairly common and you need them on when you are NOT in the truck and when it is NOT running!

WTF?.....Trucks for years have had their 12v charge system tied into the truck running!...the 12v system is NOT to run interior lights, AND it never was!
It's there to charge the on board battery that modern trailers have during towing...that's it...
Install a small battery..and light up your life

 

[TXRaptor]

That seems like a very narrow use case of the 12V to a trailer. If you are in the truck with it running, why would you need the interior lights to be on inside the trailer? Someone at Ford did not think it through, as interior lights on a trailer are fairly common and you need them on when you are NOT in the truck and when it is NOT running!

WTF?.....Trucks for years have had their 12v charge system tied into the truck running!...the 12v system is NOT to run interior lights, AND it never was!
It's there to charge the on board battery that modern trailers have during towing...that's it...
Install a small battery..and light up your life

Thanks for the clear explanation. That makes perfect sense and shows you how much I know about trailers...

 

[BlazinPond]

Ironic.
I have a new trailer and I don't understand why sometimes the trailer interior light is on, and other times not.

It's driving me crazy.

Appreciate all the input to figuring this one out.

 

[sfckelley]

Do you have an 802a? If so, you have to leave the key fob inside the truck and close the door. That’s the only way my trailer interior lights work.


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[BlazinPond]

Do you have an 802a? If so, you have to leave the key fob inside the truck and close the door. That’s the only way my trailer interior lights work.


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Yes, 802a.
That is crazy odd.

 

[pastorwug]

My 7 pin trailer cord does not go all the way into the truck receptacle unless I REALLY push it! The large center pin had trouble for some reason.
Get some electrical grease and make sure it's all greased up - that helped me.