Ut sounds like your wirirng harness isn't color coded so it might take you some extra work to figure everything out. If you don't unbundle your wires, you'll have to figure out which wire of the right length goes between the two places you need to hook it up. you could do that with a test light, a wire and an aligator clip. Put the harness through the firewall. Clip the accessory end of the wire to a hot lead from the battery. Go inside the truck, ground your test light and start touching the various candiates for the right wire, the one that lights up will be the right one!
Sounds like you smoked your fuel guage or your sending unit, or both. If either one was 6v its toast.
If the engine turns freely, and your generator is okay, provisionally wiring it to run shouldn't be hard.
Check the line from the generator/Alternator to the ammeter to the battery/starter post.
Check the line from the starter post to the ignition switch.
Check the line from the ignition switch to the coil.
Check your grounds (bat-frame, engine-frame, frame-body)
The ingnition switch on my truck has three posts. One is hot in from the battery and the other two are hot when the key is turned. It's easy to figure out which is which with a VOM. Just figure out which one doesn't flow when the switch is off and hook your hot lead to that one.
