I rewired my Mustang this morning, and I think it's finally perfect. My configuration replaces the bridge switch with a 3-way Pickup Selector (Bridge, Bridge + Neck, Neck), and it replaces the neck switch with a Parallel/Series switch (Parallel, Parallel, Series--yes, it's slightly redundant, but it's a Mustang), where in the Series mode, it completely ignores what the Pickup Selector says and just gives you glorious Bridge + Neck in Series. So this is something that's super easy to use and great to use live, because you can, say, use Series for a fuzz solo, and select a tone to switch right back into when you're done with your fuzz solo. No Morse code to try to figure out like most other Mustang wiring diagrams I've considered.
Best part? Your guitar remains completely stock from the outside, and it retains the character of the Mustang while giving you that Series sound, which by the way is how early Duo Sonics were wired, but you probably knew that.
Actually, even better part? Your guitar will never go silent unless you turn the volume knob down. You can finally be at ease with your guitar switches. The worst that can happen is you end up in another position. Your guitar will never turn off accidentally.
By the way, if you don't like the redundant 3-way Parallel/Series switch, and have access to create a new pickguard, then you can route for a 2-way switch (like from a Jaguar) instead, and just eliminate the rightmost two terminals.
If you must have phase options, then I suggest using a Push-Pull somewhere in the control cavity to reverse phase on the Bridge pickup, and have the output from the phase switch replace the Bridge pickup leads in my diagram. It'll cause a bit of a mess of wires, but that's how it goes. Or if you are building from scratch, you could always install another 2-way switch somewhere on the pickguard.
Hope this helps somebody!
