The following circuits are in MultiSIM.  I am not an expert on programs like this, but it is based on PSPICE, so I would imagine these files might work on other, similar circuit modeling software packages.  Let me know if you have any success with these on other programs, and I'll share that info.

Note that in these models I set the output of the two (or more) "pickups" to different levels.  To me, this makes it easy to see whether they are summed (i.e., connected in series) or if you're getting the reciprocal of the sum of their reciprocals (i.e., connecting them in parallel).  You can also see if you're getting phase cancelation if they drop.  If both "pickups" had the same output level, then reversing the phase of one would result in 100% cancelation or zero output, and this would be indistinguishable from a switching combination that simply grounded out the signal entirely.

In all of these circuits, the pickups are modeled using a voltage source, an inductor, and a resistor.  These are not intended as actual models of any real-world brand of guitar pickups (although the values of the individual components are, in fact, reasonable approximations of the equivalent elements of the pickup), merely as sources of sine wave signals to run through the circuitry.

The output is run to an oscilloscope so you can measure the levels to see if they are what you expect.