Need some input here.
inhave a 1993 wellcraft nova. Has a sbc carb. It stall going into revere only. When I start it and put it into forward shifts and revs up. When I shift into reverse it will shift but once I give it throttle it shuts off. Now if I disconnect the shift interuptor it will shift and and rev up fine. But soon as I plug it back in it shuts off. Never had this issue before hand. Untill end of last year. I pulled everything apart(shifter assembly) week back and it all looks fine. Moves fine. I think it’s the interuptor but I’m not 100% on how they fall. I get how they work. But don’t know why it failed! Thanks

If shift cable has too much drag, requires a lot of effort to shift, it will screw up the shift interrupter and cause troubles.
May be time for a new cable, if current one is adjusted properly.
I had an OMC King Cobra that did that years ago.

I prev had a boat with an Alpha drive and shift interrupter. The lower shift cable got stiff and caused the issues the op is seeing. Replaced the lower shift cable and it was all good.

I did think about that. But wasn’t 100% it Don’t seem to hard shifting. But I guess it wouldn’t hurt to do it anyway. It only happens in revers. Not forward. But then again one way is being pulled and one is pushed. So if it’s being pushed it would be harder. New cable it is. I will deff report back hoping this helps someone else. Thanks guys.

Routing of the lower shift cable is critical. Take pics before disassembly or some tie a string on the old one as it's being pulled out so the routing is still clear and re-installation is easier, especially if you are working alone.

So why don`t you just leave it off. Seems like a real simple fix to me.
You shouldn`t be reving it in reverse anyway.

If alpha drive it needs the shift interrupt to shift properly. The alpha drives cant shift properly without engine power being shut off momentarily when going into gear. You will wreck the gears very quickly if shifting constantly without engine power being shutoff during the shift

Ahh okay that makes sense.
I used to start mine in gear without issues and shift without interupter but I never had an alpha drive

As far as I know alpha drives are the only ones that need engine power shutoff during the shift. But I'd be willing to bet other than old seals not being replaced, high rpm shifts are the biggest killer of alphas. Other than too much power of course..

To install shift cable..,

Great reads/instructions:
http://www.mercstuff.com/shiftcable1.htm

and to adjust shift cable….:
http://www.mercstuff.com/images/shiftcable.jpg