Thanks to you all for your good advice. I played for over 50 years with electronics at a hobby level, survived lots of shocks... and even accomplished some amazing projects. Such as... turned an old 120-button accordion bass into MIDI via some 250 diodes, building two JANKO keyboards, etc.
High voltage/ ampere wiring requires correct cable thickness and mechanical joints.
Besides, the pushbutton under the seat is 30mm in diameter very flat and my body weight will securely keep it in a push-down position. If not, I can swap it for a PB, which has a 3cm switching path, such as a pneumatic house floor PB. I still got a few of these. They are now hard to find and nearly $100 (!!)
Maybe there's another way of triggering my presents, such as a light beam?