I've done quite a bit of wiring, (but not a pro) This is my opinion. (My 78 PU is similar wiring wise) Run a heavy wire from the battery (fused) to a DPDT switch, middle terminal. Personally, I would avoid tapping off the fuse block, but that's my preference. The switch should be off in the middle position, and momentary in either of the two ON positions. Run 2 wires to the tailgate, and splice to the two power leads for the window motor. You might have to run a ground wire for the tailgate as well. Now hook the wires to the switch so up on the switch is up on the window etc. On my truck, its easier to run the wires (front to back) along the frame, supported by ties, and protected with rubber tubing where it rubs metal. Just be sure to protect the wires from anything that could damage them, and short them out, or blow the fuse. Also, You could use a metal "L" or bracket under the dash to mount the switch, using existing screw holes. My truck has switches, and airbag controller crap under the dash, and I didnt have to drill any new holes. (Airbags for camper- not lowering) Greg