I recently had my adventures with the starter on my car. But, in an exactly opposite way. It activated the starter with the engine running !!! Starters and the battery suffered. I off f lucky in that the teeth on the flywheel survived
Issue was two fold
Bad ignition switch did several odd things, including combining crank and run!!!
The start relay as wired in my car needs two diodes. Just why, a bit fuzzy to me. But, seen as a back feed gate!! The new relay I installed had none!!! Replacing the one with them along with a new switch, starter and battery and all went well.
Think relay and how they work. Here we have a load circuit. Volts in and volts out.
And the trigger circuit. Prove power to one lega nd the other to ground sand the load circuit is triggered. Starter, in this case cranks.
Control here is via the inhibit switch. Some jags have it on the BW transmission Dual function switch. Also for reverse lams. Otyhers mount the same or similar switch on the switch tower and function the same way. And yet another use the micro switch at the front base of the shift tower. In that case, the micro only is involved with the starter.
So, here, I do not understand a volt reading on the ground leg of the start relay. Issue in the relay with a minor short ?
When into my adventure, I added an emergency/convenience crank wire. One end at the solenoid atop the starter. The other end up top with the bare end capped. Thusly, I can tough that bare end to battery +, which is near by, and the engine will crank. It cares not as to the position of the ignition switch. Beware, if in run, the engine will fire. In gear, not good…
All before quite useful. My vote s for a bad or misaligned micro switch…