Intermittent starter issue...

I'm an experienced mechanic but new to boating, this is my first, a 1996 Supra Mariah (yes it is actually a Supra boat), it has GT 40 engine and and the first time out it had some starter issues (of course it worked fine on the test drive). Sometimes you turn the key and it won't crank, sometimes it would. My worst fear is being stuck out on the lake so i decided to just eliminate the big stuff, got a new PCM starter, that wasn't the problem. Then i did some actual diagnostics and it seemed the solenoid located under the metal plate on the back of the engine wasn't working, so i replaced that. I was also was concerned about battery issues, so went ahead and installed a dual battery set up, with a perko switch.

Worked great, had the boat out a couple times and no issues. Then it happened again, turned the key and it would not crank? I can hear the fuel pump when i turn the key on FYI. I did the old screwdriver across the starter, and it fires right up. Works fine the rest of the day, but just to be sure i changed the ignition switch also.

Then it happened again the other day, ran fine for most of the day, and then went to start it to load on the trailer and it wouldn't start. Did the same screw driver trick and it fires right up?

Any ideas on where to go now, i don't see any sketchy wire connections? Its odd that once i start manually with the screw driver it seems to work fine?
What are the two box shaped relays on the back of the engine? I had thought they were for the fuel pump?

Sorry for the long post....

I know the exact problem you are having.... I have a 97 Sunsport. I have had the same issue you are talking about for over 15 years. Little gremlin that only shows its head every so often. I have found that typically it never does this on a cold start. Also, seems to happen more often if there is excessive moister within the boat. Has never left me stranded... "knock, knock, knock". I came to the conclusion years ago that it was the neutral switch on the transmission. I bypassed it and never had the issue again. I replaced the switch with a new one and problem started again. Next time it happens again try bypassing the switch and see if it fires right up.

Thank you, yes the neutral switch seems to be the issue. I didn't have a way to bypass yesterday, but moving the shifter in and out of gear a couple times solved it. :)