So I recent bought an American Deluxe HSS Strat and after playing it for only a couple of days (only in rehearsals, haven't even played it at a gig yet!) I discover that the S-1 switch doesn't seem to be working. When I press it, it's almost like the pickup loses the signal entirely and all that I'm left with is a thin clean tone at a very low volume, and this remains the same for all pickup selections except the bridge humbucker. My other issue is that I ordered this guitar online in the States, but I live in India so can't really just "take it back to the store!". Please help, how and why is this happening, and what can I do to fix it?

You surely encountered a bad wiring issue or a similar kind like this.

Check out the ground wires, I believe the problem is merely due to poor soldering or improper shielding.

You may want to try some electrical contact cleaner. Spray it into the switch and press it up and down to try to clean it a bit. This may or may not work but is the first thing I would try.