'74 Commando Won't Turn Off

Hello. I have a 1974 Norton Commando. Using a Podtronics system, I am negative ground. Overall a very strong runner. So I run battery positive to my key switch. Key switch to the stock voltage drop with 2.4 ohm resistance. Then + to my Boyer Mk 4. Bike won't turn off when key switch turned to off. (aftermarket key switch). So today I installed an on/off switch inline on the twelve volt to reducer. What I read is when key turned to off, the voltage does not cut power.
Instead power incrementally lowers and lowers. 12v to 8v to 6v to 4v and then engine will stop. Generally that is. Is there maybe a condenser or capacitor somewhere that may be storing charge for the next go? Perplexing.

Why not install a keyed switch that just cuts power, without all that voltage reduction crap?

I don't understand the "stock 2.4 ohm resistance". The only stock resistor on a Commando is the ballast resistor for the coils and that should be removed if you use Boyer ignition. Your wiring must be non standard if you have negative earth. Did you modify it? Switch should basically remove power from everything when off.