I wanted to do some bass experimenting, so I took my OLP MM2 and decided to throw in a SX jazz pickup I had lying around, and adding a 3 way switch in order to switch J, J&HB, HB.

I used this as a guide. http://static.zoovy.com/img/guitarelectronics/-/wdu_hh3t21_01.

Everything is soldered as it should be, but I get horrible buzzing when the tone knob is set anywhere above 0. Also the volume seems to come in the last 1/4 turn of the volume knobs instead of gradually as they should.

Any help is appreciated.

FWIW:

that's a guitar diagram with a guitar type switch which I'm guessing is what you're using instead of the typical DPDT switch found in basses. Probability is it's a wiring issue.

You might check out FAQ Dimento's Trouble Shooting Guide. In accord, with two volumes the switch is redundant so you might think about ditching it and simplifying the circuit - and/or replacing a volume with a blend to retain the speed of the switch if that matters.

Fixed the problem, and all I had to do was switch a ground. The All Parts 3 3 prong jack had me confused, especially because there is no diagram to help you figure it out. 1 prong for live signal, 1 for grounding electronics and 1 for a bridge ground. I don't really understand how that works, but all the scratching noises and problems I had are gone.

Fixed the problem, and all I had to do was switch a ground. The All Parts 3 3 prong jack had me confused, especially because there is no diagram to help you figure it out. 1 prong for live signal, 1 for grounding electronics and 1 for a bridge ground. I don't really understand how that works, but all the scratching noises and problems I had are gone.

FWIW:

then the issue would have been a grounding problem with the original wiring not a need for a change in jack. The only difference in a a stereo and mono jack is a stereo jack has one hot terminal and two ground terminals. Primarily used for actives were the one terminal (battery ground) is only tied into the circuit when the plug is place so that removing the plug prevents the battery from draining. Jacks are addressed in the trouble shooting guide.