Fender Stratocaster SH-8 Seymour Duncan??

[duncan25]

Hi guys. Just inherited a Fender Strat MIJ 1987 Model with a custom pickup. I have done some research and i think its a SD SH-8 Invader type. The question i have is that there is a switch to the right (see pics) that does not affect the sound whatsoever. Now i believe that the SD is a passive pickup as there is no battery in the back but i cant be sure due to this switch b/c a friend of mine says its for active switching.

If someone can give me some feedback regarding this it would be greatly appreciated. I took it to a guitar shop to replace the strings and get some maintenance, im still a novice player/owner , and he wasnt sure what the switch was used for either.

Your help will be greatly appreciated