Recently installed a new MSD ready to run distributor to my boat, in place of stock distributor with thunderbolt 5 ignition.
MSD ready to run distributor has 3-wires, orange wire to coil negative, red wire to coil positive and black wire to ground.
Can anyone tell me how to connect my boats shift interrupter wires to my MSD ready to run distributor wires?

No idea on that one, but wondering why you replaced a near bulletproof Merc TB V setup with a failure prone MSD??

Call MSD in case. In meantime, i’d be willing to bet you hook tach wire to the interupter like those with DUI’s (hei’s) do.
D.U.I. distributor wiring Alpha One

intellatronix has an msd replacement with a life time warranty and its made in the usa thinking of replacing the msd boxes any one run their stuff? they have an impressive web site

Thunderbolt V unreliable, hard starts and part discontinued.

You’re welcome lol

Talked with Holley dealer today, where I purchased ready to run distributor from and tech said to run the shift interrupter to the negative on the coil. I'm a little skeptical but I'll give it a try.

I ran the shift interrupter wire to the coil negative. Haven't put boat in the water yet to test but will be doing soon. Thanks everyone for help.