pickup problem.
 

i picked up a set of new pickups, DiMarzio DP126 for my Fender Aerodyne Jazz bass(P/J configuration), now I don't know how to solder but my mechanic friend does. so i had him solder it up for me. now the problem is that when i turn the volume pots its scratchy, the split pup is the only one that works, and if you tap the cover on the back it can cut the sound out for a minute...i'm thinking we got messed up in the wiring somehow. any idea where to begin?

Honestly I would just take it to a tech as is and let him take care of it for you that's a nice bass grab a pawnshop beater and learn on that in the future.