Guitronix - usa
Use a 3 pole 4 position switch for a two pickup configuration. Actually there are many ways to apply this switch. One example is the EB3 bass it uses a 3 pole 4 position rotary switch and adds some tone capacitors to filter to the desired frequencies. You can view the EB3 design here. EB-3 series #1 & #2  You can also use different caps and design a harness for guitar using the same principles. Here is a basic design of a 3 x 4 switch being used as a simple pickup switch. Options aside from each pickup you can wire parallel in/out and or series in/out you can tweak some tone by adding capacitors or choke.
This design gives you neck, neck/bridge parallel, neck/bridge series, and bridge. If you follow the positions and see what is going on with each position you can see it would be easy to ad alternatives such as split coils reverse polarity and so on. 

 Custom varitone harness for a 2 volume 2 tone configuration. Pre soldered drop in for les paul or 335 types. Install harness connect input wires to pickups or pup switch and output wires to jack and you are done  Built to gibson specs modified for less of a db cut than the standard gibson varitone.

Rewired my P jazz hybrid. I am using a 3 x 4 rotary switch for the pickup switch. #1 bridge, #2 bridge neck parallel, #3 bridge neck series out of phase, and #4 neck. From there to a 6 way varitone then to a master volume and master tone. Everything sounds great. I especially love position #3 the out of phase pickups have a nice distorted growl. Everything works just as expected.  It would also be easy enough to change pos #3 to series in phase. I always have loved the jazz bass though one thing I never liked was 2 volumes. It is an easy fix though and opens up a space for the pickup switch. I built this bass out of spare parts  it has a precision 5 string neck with an Alvarez 5 string body that was routed for the Precision pickup and the jazz bridge pickup.  I have rewired this bass at least 5 times and this is my favorite scheme so far. It has all the options I could ever want in a bass.

A new harness build for a fender jazz using the stacked CTS pot for V V a bourns 18mm guitar pot for tone and a custom 6 way varitone that all fits in a standard jazz cavity nice and neat. Let no tone go undiscovered.

Here is a design one of my customers came up with.  A custom for a jazz type bass two single coil's It incorporates 2 push pull pots and a varitone. You have a master tone plus the varitone a volume for each pickup and the push pull function allows you to switch pickups to parallel/series I am going to rewire my Precision/jazz hybrid like this one to see if I can get the same desired effect. Also on the Varitone we are trying a .1uf instead of the standard .22uf in position six