2007 Expedition trailer wiring question

[mdcarter30]

I just picked up a 2007 Expedition and am currently upgrading the tow package to the heavy duty package.

My question concerns the wiring. I have the flat 4-way and need to upgrade to 7-way. There is a wire next to the 4-way labled "Elec Brake", so I'm good with that, but I cannot find a wire for the charge circuit. I have the fuse and relay to go in the box under the hood, I just cannot find the wire to add to the 7-way. I would like to stay with factory wiring on everything and not have to run new wires.

Can anybody help???