I have a 2009 f150 and tow a 24 ft car hauler - I use a 7 pin connector.

My question is this: I have a car battery mounted on the trailer - it's connected to some lights inside of the trailer to provide some light inside of the trailer when I don't have any electrical hookups.

the battery, of course, needs to be charged.

I tried hooking up the middle pin with a wire to the positive terminal, but I wasn't getting power (I tested with a test light), grounding to the battery's ground which has a ground strap attached to the trailer.

Can someone tell me which pin that I need to connect from the harness to the battery that I can get a charge from the truck? Or what I need to do to get it to charge the battery while it's hooked up?

Thanks

 

The center pin is for reverse lights I think. The one you want is the "+" pin and I think it's in the 1 o'clock position. The plug cap should have a diagram listing all the pins functions. On the trailers corrosponding pin for this one, make sure it goes to the batteries "+" post. This should charge the battery while your truck is running.

You must have the key in the "ON" position for this pin to work too. (this is so you don't drain your trucks battery if you leave the trailer plugged in.)

Mitch

 

Correct of the wiring MitchF150.
Looking at the truck plug the positive is in the 1'oclock position.

No need to wiring anything differwnt when using a 7 pin trailer plug.
The center pin was factory already wired for reverse lights like all newer verhicles with a factory 7 pin.

 

Some guys on an RV site told me it's the number 4 pin which is located at the 11'oclock position. This is the dome and battery charge light.

See the diagram below.

http://www.offroaders.com/tech/trail...ng-diagram.htm

Thanks for the help

 

That would be correct for the TRAILERS plug as you are looking at the face of it.

I was talking about the TRUCKS plug and the + being at 1 o'clock so everyone is correct!

I suppose it's all in how the trailer is wired as to where that pin goes.. It could go directly to the dome light in the trailer in order to power those while it's plugged in... If the trailer has a battery, then it should go to that and the dome lights would be powered from the trailer battery.

Mitch

 

That second schematic down is one of the craziest one I ave ever seen yet!!
The 1st one really isn't even used any more but by very few trailer manufacturers.

None of those show the most common 7 pin color wiring used in new trailers today: Depending on colors in wire group.

Ground White or black
Left turn/brake Yellow
Park/Running Brown
Right turn/brake Green
Electric Brake Blue
Charge Line (+) Black or red
Reverse Orange or black (most commonly ommited wire)

 

I just had to deal with this myself. Everything worked except no (+) on the (+) pin (correct pin should be marked on the cover, at least it is on mine).
I went to the Ford dealer today and a mechanic helped me out. There is a relay that is needed to supply positive to the plug and apparently, even though the truck has a factory-installed tow package, the factory doesn't always install this relay. The mechanic scrounged up a relay and installed it for me (at no charge), now my battery will charge while I'm towing my trailer.
Thank you to Sunland Ford in Victorville, CA.

 

Are you talking about the relay that comes in the ziplock bag that was located in the compartment in the driver's door? That came with my truck and I installed it - I'm not sure why they don't just install it at the factory. - I'm sure there's some cost cutting reason.

 

The reason is 2 fold.
1st most people never tow anything and don't need them installed.
2nd in states where it snows and salt is used, by having exposed hot connections they tend to corrode in the weather. By not installing them in every vehicle you prevent wire corrosion in vehicles not used in towing.

 

I guess that would be the relay. I bought my '07 used so if there had been a relay it was long gone. It would have been helpful if the owner's manual would have mentioned it and I guess if I had paid more attention to the fuse panel layout, I would have picked up on it, all I checked was the fuse. If they put the relay in a baggie in the new trucks, that probably explains why the mechanic was able to scrounge one up out of their ditty stock instead of me having to buy one.