Cop spec M bodies had an electrical part throttle unlock solenoid that allowed the TC to unlock based on throttle input. Lockup functioned just like the civilian version.
This would be the only case in an M body that would have had anything electrical to do with lockup. Right up to 1989 the only thing non-cop ones have is the neutral safety switch and everything else is done within the transmission itself.
Mitchel On Demand wiring diagrams for BOTH '88 and '89 Diplomat SE's show a "Part Throttle Unlock Relay" - receives ground signal from the Spark Control Computer (org/blk wire - plug 1/pin 8), and 3 dark blue wires - 2 provide signal and input 12v+ (same dk blue wire from key that powers the coil, volt reg, alt field, etc.) , and 1 providing the 12v+ output from the relay to the "Part Throttle Unlock Solenoid" in the trans.
So, according to Mitchel, controlling the lock-up electronically started in '88.
