Electricity is dangerous, so if you don't understand the circuitry,
don't do it yourself! What you want to do is probably best left to an
electrician.

You have a 2 wire system. Line and load. Line is the "hot" wire.
Load is the "neutral" or "ground". The terminology here can be vague,
so be careful: there is a difference between grounding and grounded.
What you have here would normally be a white wire in modern wiring.
What you are missing is the bare wire, or "copper" wire. The missing
wire is also why you have 2-prong plugs instead of 3 prong plugs for
your electrical outlets.

I like the older terminology better. You have a hot wire and a
"working ground". You are missing the "mechanical ground".

If you are heart-set on that switch, you could have an electrician wire
a mechanical ground for you and install the switch. But your load is
pretty big so it would be much better to have the electrician rewire
the whole circuit. In fact, that switch should probably be on its own
breaker.

Good luck with it.