The switch guts are covered by glue, but it appears to be the second finger hole down in the picture. I can't tell if it's a pressure pad electronic, or electircal contact switch. There is also what appears to be some type of possible electronics in a small box between the switch and the negitive spring. Again, I could be wrong. Is there some sort of protection fuse there?
However, I agree that the positive pin and 510 NEED to be upgraded! LIKE NOW. I would be very nervous with a charm as a positive pin!