Your best bet on the tuners is the HipShot Ultralite as seen above. They are wonderful tuners and are incredibly light. They come in 2 different shaft sizes and it would be best to pull a tuner off your bass and measure that before ordering.
John Wymore's Store Site
John has the tuners in both sizes listed so there is a place you can find the sizes. Not sure if he ships internationally or not. He's been my go to for the parts I buy for a while.
Far as the wiring goies - of the pickup works, then the circuit has to be complete... If not, maybe the ground lead came off - wouldn't be the first time that happened. Sometimes, most of the time actually I've been lucky and able to reattach the lead.
Blend knob's on passive basses... not usually successful IME. Often there is a noticible change in vol and tone with the control centered.
On passive basses, I prefer Vol/Tone & Vol/Tone or the traditional Vol / Vol / Tone personally. The V/T V/T setup is a little darker and often that isn't a bad thing. We play bass not treble after all