just wrapped up rewiring my 46 one ton with a ez wire harness.I used 3/4 " for the wires going through the driver side firewall.1/2" for the rear lights,and some 3/8" for some of the guage and coil wires.As far as how much, i would measure your runs and add about 20%.I was happy with the quality of the harness for the price,about half of painless and most others.the printing on the wires every 5" is a big help.Good luck,take your time and if you don,t have one get a good soldering iron and lots of assorted heat shrink tubing the kind with adhesive liner not the cheap crap.
