I have a 2004 F150 XLT Supercab with 52,000 miles. I was cleaning it out today and noticed the a ziploc bag that came with my truck. After I started to read it I noticed it was a "Trailer Tow Relay" & it was supposed to be in the fuse box in as Fuse#5.

What is this fuse actually used for & why wasnt it already installed when i bought my truck????

 

i just bought an 07 and mine has it in the drivers door in a bag...never really payed any attention to it.

 

yeah, my 06 has it too, i heard that it is a spare for the trailer plug in the back of the car...

 

Not really a spare, there is no relay in it's slot. I don't know why Ford doesn't install them from the factory. If you are going to do any towing with electric breaks you will need to install it in the fuse box, passenger floor kick panel. The pigtail will need to be wired up with a controller and plugged in under the dash.

 

Ford dosen't instal it because only a few people use it, and they can save money by not having to install the extra wires.

 

Wires are already there if you got the tow package. The relay isn't installed though. The pigtail is to wire up with what ever brake controller the owner decides to use for their setup.

 

what do u mean by the pigtail or w/e...do u mean that big thing thats made by delphi that plugs into the round part of the hitch plug?? and you say that the fuse box is on the passenger side kick panel? thats inconvenient...

 

The Pigtail is the thing in the bag that has 5 or 6 wires attached to it, looks like it needs to be wired up to something. The relay is the small square thing that plugs into the fuse panel. The fuse panel has a door over it that you have to remove to access it. Look at the kick panel on the passenger floor and you'll see it.
Does your truck have two connectors at the hitch to plug into (one round and one flat) or just one (round)?

 

does it hurt to just put that relay in no matter what, ill prolly hardly ever have a trailer on the back, let alone one with electric brakes.

 

I don't see how. I always leave mine in. In my last truck (for 4yrs) and now this truck. Never had a problem. One plus is if you ever decide to add some back up lights The relay will supply 12v to the center post on the round connector everytime you put it in reverse. So it makes wiring them up real easy. I tapped that circuit for my reverse camera.