good eye man!!
i had a similar problem, my stock sub just quit workin one day and i could not figure out why, i tried to take it apart and looked at all the wires and stuff but no luck.
and for about 6 months i rode around with it not working, and one day i decided to look in the fuse box and found that the factory sub fuse was lose and just popped it back into place and it worked
but then i got an aftermarket sub