I moved this thread from Dockside Chat.
The shift interrupt system has nothing to do with shifting into gear, only coming out of gear while in the water.
If it's grinding, either the idle rpm is too high, you are shifting too slow, or the cables are worn/binding/out of adjustment.
I always find this thread useful in times like this:
http://forums.iboats.com/mercruiser...nterrupt-system-works-288089.html#post1930449
Thanks, i was trying to figure out how to fix a spelling error and move to the correct spot.