Mercruiser Shift Plate Kit Problem

[Boatrunner1]

I have a 1995 Mercruiser 5.7L I/O engine on a Larson Escapade 240 Day Cruiser. Sometimes when shifting out of forward into neutral it would stall. Shifting out of reverse into neutral doesn't ever stall. I decided to update from the original roller type shift interrupt switch and install the upgraded new style shift interrupter plate kit. As the directions mentioned I did not make any cable adjustments when installing the new shift plate kit. I started up the boat and let it run to get it up to temperature before trying to test the shifting in and out of forward and reverse. The boat was idling fine and reached temperature and while I was tightening the ropes at my slip, to be able to put the boat in forward and reverse tied t my slip, the engine suddenly just shut off as if the key was shut off. No rough running prior to it shutting off.
I did notice that the idle speed slowed down to about 600 rpm from the 900 rpm that it was at temperature (140). It ran at the 600 rpm for about 5 minutes before it shut off. I turned up the idle screw a half a turn and pumped the throttle and attempted to restart the engine. I could not get it to restart. I made sure it was in neutral but it was as if no spark was being generated at all, no gurgling no sign of it trying to start. I then unhooked and cleaned all of the electrical connections, ground connections and battery terminals. The next day I attempted to start the engine and it started up. I let it run for abut 15 minutes (900 rpm in neutral) and suddenly it shut off again as if the key was shut off (prior to me putting it in or out of gear).
I'm thinking now that the shift plate must be depressing the switch very slightly when it is running in neutral and then a little vibration is causing it to shut off the engine and that I need to start from scratch and adjust the shift cable etc...
I'm thinking that unhooking a wire from the interrupt switch will probably enable me to start the engine and have it run without suddenly shutting off. Then if I take the shift cable off the shift plate and manually push the cable in to put the boat in forward gear (with the engine running) I can measure and adjust the 6 inch middle of the barrel to middle of shift rod hole measurement. Then with the motor still running and in forward gear I could then put the remote shifter handle into the forward gear position and mount the gear cable onto the shifter plate?
Alternatively, if I shut off the engine with it in forward gear and then moved the remote shifter out of neutral into the forward gear position and then attached the shift cable to the shift plate would the clutch dogs still remain properly engaged in the forward gear position or would they separate when the engine is turned off?
As I mentioned earlier the boat is in the marina at a slip which presents a challenge trying to adjust the shift cable etc...
Anybody have any ideas about what happened with my boat and how to fix it in the water?
Thanks...

 

[alldodge]

The interrupter switch is to make the motor stumble so it can be taken out of gear. If its disconnected it will go in gear, but will not come out very easy if it does at all

Adjusting the shift cable is normally done with the motor OFF and the switch is done that way also, just place in the center of notch

 

[Boatrunner1]

Thanks for the response. The challenge is that my boat is in the water at a marina and there no practical way to turn and hold the prop to get it in forward gear and hold it there.