After getting your mounting place decided upon and installed, start the wiring job by mounting the panel first. Look at where the wires need to go in relation to what they are for. A little preplanning here goes a long way in the finished job. Do you want the wires to be hidden from view when installed? Where can you route them best to get them to do what they need to do. For the F-100s and most any other car I've wired, they all basically go the same route. From the fuse panel, my engine wiring goes along the 1x1-inch tube to the center of the vehicle and then drops down through a 1 1/4-inch grommeted hole at the top of the tranny cover on the passenger side. This puts the wire loom at the back of the engine with the wiring coming down the engine on the passenger side and wrapping around the front of the engine to hook up the alternator, A/C, distributor, temp sender, and others. The starter wires drop down to the starter and in the case of the F100s, the battery hots are routed to the battery box under the passenger floor. With the front seat removed, I sit on the driver side and cut the coiled up looms apart one at a time. Usually first is the looms for the front and rear wiring. I roll out the looms one at a time on the floor next to the truck and pull out the wires that are going some other place. Then using some tape I tape the loose ends of the wire loom together so the loom is easier to feed through the body and grommeted holes. Then I do the engine wires and route them over to and through the hole at the bottom of the firewall. Last is the dash wiring, which I route along the bottom of the dash. Loom the wires together with a few zip ties and lay them on the inside of the dash. Decide where your switches are going to be and stub out the wires for each switch from the loom.
The front and rear wiring looms are routed over to the driver-side cowl area just in front of the driver's door. They are hidden by the driver-side kick panel when installed and exit out the bottom of the cab right under the front cab mount. They then run across the front cab mount and split off to the front and rear on the inside of the framerail. If the customer is using a reproduction chassis that is fully boxed then I hole-saw the side of the rail and route my wiring inside the rails for as far as I can. Small holes are drilled and grommeted to pop wires out at places like the brake light switch, electric fuel pump (if on the rail), and such.
On a stock chassis the rear wire loom pretty much follows the brake lines and is zip-tied to it for mounting, or you could drill and mount clamps along the inside of the framerail to attach the loom. The front wire loom with the lights, fan, and horn wires is routed up the wheel side of the inner fender and attached to the bolts that mount the inner fender to the fender. I make small tabs that bolt to the inner fender bolts and then the loom is zip-tied to the tabs. The loom drops down from the top of the inner fender at the air deflector shields and splits off there for the driver-side headlights and turn signal. Then the loom is run across the front of the bottom of the radiator and over to the passenger side where it goes up the air deflector shield and in to the passenger-side headlight. I zip-tie the loom to the metal brace supports on the backside of the gravel pan. Always start from the fuse panel, working your looms out to where they are going to end. Secure the looms along the way as you run them, then hook up whatever the wires are going to last.
Testing of the lights, fans, and others, for the proper wiring of them is easy with a 12 or 14V battery from your battery-powered drill. You can test electric fan direction, turn and taillights and hook the wires up right the first time. I've also used an automotive battery charger to test with.