Wiring humbucker to toggle double coil, single coil and off?

[Andrew Roblin]

I'm cleaning and refurbishing a Link II pedal steel by Linkon.

It has a humbucker pickup and a three-way mini switch. Right now, the switch only toggles through on, on and off.

How do I wire the switch so it toggles through double coil, single coil and off?

Thank you.

[Lane Gray]

There are several configurations of SPDT switches, so it won't be simple to say "do this".
My favorite mode is to use a simple SPST (Single Pole, Single Throw).
For your 705, black is neutral and white is hot (or do I have it backwards?). The red/green pair goes to one side of the switch, and you run a wire from the other side of the switch to ground.
When the switch is open, it's a humbucker and when you close it, you short one coil, leaving just one