Rear window defroster

Well, how many connections does your rear window element have?

Probably only 2. One for ground, the other for power.

If the switch has some sort of power reduction resistor (which I doubt) then you could have a two setting rear window.

I would recommend running a relay to power the window unit and use the switch to actuate the relay so as to protect the switch and keep it from melting or the contacts from burning out prematurely.
This way you would just hook H to the relay to trigger the relay, and the relay would have its main to power the window.

Very cool setup you have there.

Where did you get the rear window? Where did you get the switch?

If you have questions about setting up the relay (if interested), I can draw a wire diagram for you and post it here. There are lots of folks on here running relays these days since they allow full power and amps to the peripheral with out being hard on your switches.