OK, you shouldn’t interrupt the red power lead coming to the ignition switch. The lead that should be interrupted is the purple lead on the accessory terminal of the key switch. (not sure how many purple leads are on this terminal on your engine though).
Keep in mind that this engine has battery CD ignition and a hydro electric gearcase, so there is some current running through that key switch at all times when running. You must be very careful to use a robust/water proof switch/wiring to avoid issues that might damage engine ignition and gearcase components. There are some strange diodes in this system also. Messing with the wiring could actually cause a shorted “blocking diode” that would prevent the engine from shutting off when the key switch is turned off. The shift diodes ensure the engine stays in neutral/doesn’t bang into forward gear, when the key switch is turned off. Altering the wiring could cause poor connections and damage the ignition system “power pack” as well.
