One of these will work. Kill Switch W/Tether Coil - iboats.com
Hooking it up is pretty simple. You have a black wire with a yellow tracer going to your switch. You need to tap into (not cut) that wire anywhere you can and hook it to one side of the kill switch. The other side of the kill switch get connected to ground. That it. Other than mounting the switch. Its important that you just tap into the black/yellow wire and not cut it. If you cut it you won't be able to turn your motor off.
Fair Winds and Following Seas
Bill H. PTC USN Ret
Chesapeake, Va