Gemini humbuckers are designed for series wiring. The two coils are connected internally in series. In most cases, there is no centre tap and parallel wiring would produce very poor results. The three conductor wiring used does not allow parallel wiring in phase. If you wire in parallel, the two sections of the winding will be out of phase.

Sequence of wiring

The sequence in which switches and controls are connected is important for successful results when installing pickups.

Pickup mode switching
Volume and/or tone if they are individual for the pickups
Pickup selector switch
Volume and/or Tone if master
Output to jack socket

Gemini pickups are compatible with most other pickups and with most switching arrangements.

Switching

3 conductor humbuckers can be used in most guitars where a coil tap facility is available, most often with no modification to the existing switching system. If fitting pickups to a guitar with a 5 way 2 pole or 4 pole switch, make sure you check how the humbucker(s) are switched. Sometimes, parallel switching is used, sometimes different coils are tapped. These switching arrangements are not possible. The same switch can be used but some re-wiring may be required.

Tone and Volume

Gemini pickups are conventional passive pickups and therefore compatible with other passive pickups in terms of volume and tone controls. They are not compatible with most active pickup systems which require 25k pots, rather than 250k - 500k pots.

Hum Cancellation

In tapped modes, all Gemini models are designed to be hum cancelling between neck and bridge. To achieve this, neck and bridge models are wound and wired differently. The primary (dominant coil when tapped) is counter clockwise north (CCWN) in the neck pickups and clockwise south (CWS) in the bridge pickups.

Standard single coils are usually CWS, reverse wound reverse polarity (RW/RP) single coils are normally CCWN. One CWS + one CCWN pickup are hum cancelling.

Complete hum cancellation is only achieved by exactly balanced coils. Tapped Gemini humbuckers have part of the second (hum cancelling) coil included in circuit. Therefore a 7.5k mode may only have a nett hum equivalent to 2.5k. If correctly combined with a second pickup of 6k, there will be residual hum equivalent to 3.5k.

Regardless of hum cancellation, Gemini humbuckers should be phase compatible with almost all other pickups. There are a small number of pickups, including some vintage strat pickups that are clock wise north (CWN).

Using Gemini humbuckers in H-S-H configurations, either the bridge pickup will be hum cancelling when combined with the middle pickup or the neck pickup will be, but not both. If you use switching that also includes Bridge+Neck combinations without the middle pickup, this probably should just be accepted.

If you do not, you can have both pickups hum cancelling by using two neck pickups or two bridge pickups. You can use two identical pickups but often it is better to use a hotter pickup in the bridge. E.g. Bridge = Gryphon neck, Neck = Vampire neck. Sonically, the Gryphon neck is almost identical to the Vampire bridge.

The same principle applies when choosing bridge pickups for H-S-S guitars.

The sequence of the leads from start to end of the winding is consistent across all designs.

4 conductor cable has red white black green

3 conductor humbuckers, all models
These pickups have one hot lead from the primary coil and two earth leads from the secondary coil

Red - full live
White - not used
Black - tapped earth
Green - full earth

4 conductor humbucker Star series
Red - full live
White - tapped live
Black - tapped earth
Green - full earth

4 conductor humbucker, Fire series & Ghost Rider

Red - full live
White - tapped live
Black - tapped earth
Green - full earth

2 Conductor Single Coils
These pickups have one live lead and one earth lead.

White (or Red) live
Black Earth

3 conductor single coil Werewolf, Seraphim, Cherubim
These pickups have two lives and one earth, one being a coil tap.