You're going to want to run the white wire from the middle lug of the tone pot to the lug of the volume pot that's connected to the jack tip (the outer, un-grounded lug).
Here's a photo of what it looked like inside my jag-stang stock:
For the jack plug - mine also came from the factory with only the tip-lug soldered!
My guitar tech added a wire from the sleeve-lug to the back of the tone pot for grounding. I haven't noticed any difference in hum before/after, but it could be worth doing!
