1975 20SF Starting Problems

[Sf20]

-My boat (20sf with a 165hp Mercruiser) left me stranded the other day. First it wouldn't crank, then it wasn't getting any fire. I had to swim it about 200 yards to a dock and leave it for the night. When I came back the next morning it started right up. We turned it off and then it didn't want it to crank at all. We had to hot wire it to get is started so I could drive it back to the marina. We have been able to replicate the problem with the boat not cranking, but we haven't really found any smoking gun. We have not been able to replicate the no fire problem. We took the throttle lever apart and checked the neutral switch and it was good. There is another neutral switch back by the linkage that operates the transmission, this switch also checked out good. It has a new ignition switch, so I don't anticipate that being an issue. Any other ideas would be appreciated. I feel like I'm just shooting in the dark, but that's how a lot of electrical problems go I guess...