RESOLVED! It was the rubber boot from that battery terminal that was touching the neutral safety and ground wire terminal. You can see it in the pic above. I never would have guessed this. While trying to figure this out, I read somewhere that these old rubber boots can sometimes get dirty...
Here's an actual photo of the new Sierra 18-5808 Solenoid wired. You'll see the cushioning band is completely degraded and so I've removed and wrapped the solenoid in electrical tape where that cushioning band is.
A legend for this photo:
Blue Arrow = Starter side of solenoid
Yellow Arrow =...
Important, I'm no mechanic! Just someone trying to help out. Anyhow, I'm troubleshooting a strange starting issue on a 1979 Evinrude 75 HP (Model 75943R, S/N J0001903) and I'm hoping someone familiar with these older OMC electrical systems has seen this before.
Last year the boat developed a...