Hi Phil,

You can try putting the ignition key in KP2 (run position) and
make a jumper to put +12V from the battery to the service port.
Use a 1/4" male spade lug to the port that breaks out of the harness
on the drivers side with a single pink wire.

If it starts then your ignition switch is the culprit with pin 50 dead.

Before you condemn the switch, go back to your positive terminal on the battery
and the piggy backed wires.
Examine the terminal ends and look for telltale Greenish blue copper oxide
indicating ratty terminal ends at the crimp. Shine up everything and reassemble with conductive grease. Nickel or copper anti seize or Penetrox.
Wire brush the battery anodes for good luck and use the same grease.

Post back with your findings, Bill