Steve Morse model – pickups in series or parallel?

I have only recently bought an original Morse (the one with the 4 pickups) as he is fast becoming my favourite guitarist! And now I know why he has stuck with EBMM for over 30 years!

However, as I am not Steve, I am thinking of making some mods to the wiring of the guitar, but I am finding it is totally unique.

I am thinking of adding a 5-way switch instead of the 3-way, but would like to not split the humbuckers in positions 2 and 4 when I add the 5-way, as the original wiring does not allow for splitting them.

So, my question is, are the original singles wired in series or in parallel with the humbuckers?

For example, when the 3-way switch has selected the bridge pickup, and I turn on the bridge humbucker, are the two pickups in series or parallel? Is the same the case if the 3-way toggle is on for the neck single coil to be in combination with any of the humbuckers?

(interestingly, on the Y2D it actually states that the pickups are in parallel in the switching diagram)

I cannot figure this out by myself to recreate it on a 5-way switch. Any help would be greatly appreciated!

Tx,
Nick