Will not start

Start by measuring the voltage on the fat wire bolted onto the back of the generator. You should find 12 volts there all the time. If it's missing, there is a break in the circuit which could include a bolted-in fuse in the under-hood fuse box. Beyond that, I'll have to dig up a wiring diagram to see where to go next.

Also check if there were other smaller wires bolted to the stud on the back of the generator that got forgotten. GM likes to use generator and starter terminals as convenient tie points for multiple circuits. There is no problem doing that as long as you get them all reconnected.

If you do have 12 volts at the back of the generator, remeasure with the head lights turned on or when a helper tries to crank the engine. We just need anything that causes current to want to flow. The resulting drop in voltage will be a clue for where to look next.