Anyone know what this gray wire is for? 2009 f150 5.4 4wd is my truck.Truck was bought used a few months back.

Finger is on gray wire.

 

Where is it located?
Under hood near...
Under dash?

 

The gray wire is under the hood right next to the front fuse box(On the righ side).The end of the wire isnt bare wire.

 

Looking in my 2013 manual which doesn't cover your engine.
I see a gray wire on fuse 56 having to do with heated side mirrors.. (if equipped)
Im not sure if thats a capped off wire for something like that.

 

I just happened to notice it today after checking fluids and changing the air filter.Never even noticed it before for some odd reason.The truck is a platinum as well.Thanks for replying,I was mainly curious about it.

 

My 2010 has the same wire. I think it may be a customer access wire from the interior harness. If you look under the dash on the left side you will find a matching grey wire capped off there. I bet if you get a multimeter out and check there will be continuity to both which allows you to add an aftermarket accessory to that point. Vehicles with optional upfitter option (SVT RAPTOR) have at least 4 customer access wires for that purpose.

 

I could be wrong and often am, but I believe that wire is the third brake light signal for an aftermarket truck cap. This way the third brake light does not blink when you put the turn signal on as it would uf you just tapped into a brake light at the tail light itself.

You would need to route a harness from that wire all the way to the truck cap.

 

wiring diagram, download Carmin app and it has everything from bumper to bumper as far as schematics go.

 

This is what I believe it to be as well.

 

Thanks for the information, much appreciated.