Here is the cable running from the dash, down the firewall, and across the carpet (it used to be under the carpet):
And it runs under the seat to the box:
Here are some photos of the box for size references:
(FYI, the cover was removed for the photo):
Blue_71 has ordered a shorter cable because he wants to mount the box under the hood. But for now it is run under the seat. It has to have a power wire, a ground wire, and a signal wire from the transmission. It also has to be kept dry from the elements (water, excessive wind, ice, snow, etc.), as any electrical equipment usually does.
Here is his interior: Now can anyone imagine why he calls this truck "Bloo"???
Hope you enjoy!
~jewels.