I have found it easier to run a new line using a good quality aftermarket blade type fuse holder than trying to track down a wire in an unknown location.
Generally, I'll take the power from a "Switched" bus at the main distribution panel, which, on my Mid-door Coach, is behind the vertical panel in front of the passenger's foot well. Can't say where it is on a front door model but I suspect the same place.
Regardless, whenever I find an inexpensive in-line fuse holder, I replace them with blade type fuse holders. If on the exterior of the Coach, I use a waterproof holder having a cover and solder them into the line.
Bob (Squidly Down Under) & Peg - 2013 Ford Focus pushing a 2011 Phoenix Cruiser 2552S
"In God we trust" to preserve our country and bring our Troops safely home.
Carry on, regardless..................