Hooking up shift cut out switch

[g123]

Hi,I have an 87 boat boat with a alpha one drive, and a 350. I changed the ignition to all msd, 7al2 box,billet dist.,and blaster coil. Now I need to how to make the shift interuptor work. Where do I hook the two wires to? I can not get it out of gear w/o shutting it off. Thanks for any replies.

[Havasu47]

The switch interrupts the ign. circuit. So the purple wire in the Merc loom you hooked to the small red wire to power the MSD box goes through the switch.