I fabricated a neutral switch on a Chevy/F*rd conversion, using a microswitch and a disc mounted to the shift quadrant on the transmission linkage at the transmission. I filed a couple of notches in the disk, and mounted the switch so its roller would fall into the low spot when park or neutral was engaged. use the "normally closed" contacts of the microswitch to engage a F*rd solenoid, and trigger the GM solenoid with that one. The GM unit draws too much current to run directly through the microswitch contacts.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!