Hey, I did just the same thing a while ago.
Took a bit of time but I found just the right diagram... I knew I still had the link somewhere...
http://www.guitarelectronics.com/tonemods.html
Second diagram from the top.
It's actually pretty easy, as long as you don't get confused by all the wires. After I had that sorted out it worked just fine, even though I didn't have much experience with soldering.
Good luck with your bass!