I just replaced both pots and output jack on a Musicmaster bass, a single PU. The pickguard does not have grd foil. I purchased the pots and output jack prewired. I feel they are right. There are no switches. I have a grd coming from bridge that is grd to pot. I have a grd from PU to pot I have red wire from PU to lead wire on vol pot. However, I have a hum. I have not put strings on. Guitar cord is good. Other guitars do not hum with amp. I disconnected PU and it still hums. I can tell that the vol and tone are working. Vol off cuts hum. Any clues?