So I recently changed my volume and tone on my (Jack & Danny) Jazz bass to two separate double pots with volume and tone to each pickup. I also added some switches for different effects (series or parallel , an effect within the bass and a switch for splitting the output to two different jacks. Everything has been fitted in the bass and the different switches do what the should, but there is a LOT of noise, buzzing and sparks and I think it has something to do with ground, but i don't know where. I crudely made a paint image to show you how it's all wired up Red - From neck pickup Blue - From bridge pickup Gray - Ground The first switch is the parallel or series -switch The second the one who chooses between going to effect or not (note that it is there the bridge signal gets mixed with the neck in parallel setting) The third one is a bit tricky. On the left side the bridge pickup signal gets in and from there can go directly to a jack (down) or get mixed with the neck signal (up). On the other side of the switch, the mixed signal gets in and also the effect signal. Here it chooses between going to a single jack (down) or to both of the jacks.