Hey Gang,
Looking for some help from this 'Brain Trust' of knowledge. Issue: 2001 502 MPI was running fine THEN suddenly the starter would not crank:
1. I replaced the starter, starter slave solenoid, ignition key switch, verified both 90 amp breakers are good, all other fuses are good, offshore shifter safety neutral switch is working properly and batteries/grounds are fully charged and no corrosion.
2. I verified I've got constant 12 volts to the Red/Purple post on the starter slave solenoid and that when I turn the ignition key to the START position that the Yellow/Red post gets 12 volts but no starter crank
3. I can jumper the Red/Purple and Yellow/Red posts on the starter slave solenoid and the starter cranks over
4. I removed the Purple jumper wire off the TACH to verify a faulty Tach wasn't causing a direct grounding

Any recommendations/directions would be GREATLY APPRECIATED!!!!

Your #3 means the solenoid is either wired wrong, faulty, or the ground to solenoid faulty. Last possibility, but more rare, yellow red from shifter neutral safety (goes to a lower smaller stud ) not enough power to enact this ‘large’ solenoid.

Use this to Double check your wiring too:

Thx for the insight I'll recheck those items!!

Update: Found the small gauge yellow/black ground wire on starter slave solenoid faulty - Repaired the wire and Vrrrrooooom!!!! THANKS AGAIN for the insight!!!!!!!!! 99.9% of any electrical issue is a bad ground wire LOL!!!!