Even that we are naming this modules as humbucker related, you should take into account that those apply to any combination of two coils or two pickups.
Remember than, even that the output negative wire is shown as grounded in all these schemes, it can be prolonged out of this module to be used in further modules.
This will be used to toggle between parallel and series arrangement of pickups or coils. See this picture:
The first scheme corresponds to the usual way to select between series and parallel. There is just a single signal output and, it's mainly used to select series/parallel within a humbucker.
The second scheme corresponds to a way to connect two pickups in series or parallel, while sending it's outputs to the corresponding pickups' selector switch.
When they are in parallel, HOT1 corresponds to output signal of the upper coil (or pickup) and, HOT 2 corresponds to the output signal of the lower coil (or pickup). When they are in series, both hots (HOT1 and HOT2) have the same signal output, that is, both coils (or pickups) in series.
This is a tricky way to avoid some blackouts on selector switch when putting two pickups in series.
This kind of wiring will allow us to choose one of the coils of a certain humbucker but, remember, it can be used to select one or other pickup, as well. Look at this picture:
The first schema is being used to split to inner coil (the one that points to the neck), in this case, the slug coil.
The second schema is being used to split to outer coil (the one that points to the bridge), in this case, the screw coil. Remember our previous discussion about this way of selecting the screw coil. It can have side effects but, the most of times it works.
First and second schemes can be implemented by using just a SPDT on/on switch but, for sure, you can always just wire one row of a DPDT on/on switch (as a pull/push pot, by example).
The third schema corresponds to a switch that will select inner coil / humbucker / outer coil.
This needs a SPDT on/OFF/on or a DPDT on/OFF/on and, it will modify the aspect of your guitar.
The good thing is that allows you to select any of the pickups of a humbucker or the native humbucker mode (on middle position).
If you wanted the 4 fundamental tones of a humbucker (split-inner, split-outer, coils in parallel and coils in series) you will need at least a 2 poles and 4 throws switch, as the Telecaster 4-way or any DP4T you can find, including rotary switches. See the picture below:
Both switches are doing the same:
Position 1: humbucker (coils in series)
Position 2: coils in parallel
Position 3: screw coil
Position 4: slug coil
But, the potential issue that we described with the split to screw coil option is still there. To make it bullet-proof, we should need a 4P4T switch and, this is usually only available as a rotary switch.
We have still one more way to select the 4 foundational tones of a humbucker by using a couple of DPDT on/on switches (that is, two pull/pushes, by example). Look at this picture:
This was designed by user ArtieToo, that you can find on Seymour Duncan's forum. A real wizard of electronics and, a wise and kind man. I've learnt everything from him.
The original design was made by Frank Falbo of Seymour Duncan' staff but, Artie improved it to reduce any potential side effect. First time I saw this tricky wiring, I was absolutely shocked.
To get the 4 positions you need to work on both switches.
When both are down, you have coils in series (standard humbucker).
When both are up, you have coils in parallel.
When one is down and the other up, you have the two splits.
Very useful, if you don't like to change your guitar's appearance.
On next part, we are going to talk about other useful things, that are more general or that include a couple of humbuckers, by example. We will discuss the Artie's Coil Swap switch, the kill-switch, the bridge-on switch, the bypass switch, etc.