Its got to be something between battery terminal, through the ignition switch to the solenoid terminal. You said it starts right up if you run a wire from the bat to the solenoid.

On my 87 740 there is a terminal just north of the battery that carries that ignition signal. On a couple of occassions it has become corroded and caused similar problems. I dont know how a 89 resembles the 87 but it could be similar.
I would definetly start checking the battery end first. Then move to the switch.
check anything that even remotely looks like a juction near the battery and runs to the passenger compartment. Corrosion can stop it in its tracks.

Also sometimes the neutral safety circuit will fail because of toasted bushings in the shift linkeage. Have you tried wiggling the gear shift lever, and perhaps trying to start in neutral.

And no it doesnt sound like it has anything, whatsoever, to do with the hall effect. That would be if it were turning over, but not starting. You said not click, no nothing.

My 2 cent worth.

Good luck,

Lawrence