Loads of humbucker-equipped electric guitars have coil-split switching options. The majority simply dump one of the humbucker’s coils to ground, leaving just one working. It can result in a rather thin single-coil tone.
PRS recently started using quite an old idea (first suggested to us by guitar/amp technician Brinsley Schwarz). You simply add, in series, a resistor between the pickup ‘tap’ wire and ground. This mod, “doesn’t completely cancel the slug coil,” explains Smith, “it sort of three-quarters coil cancels. It allows some of the other [slug] coil through. It’s also slightly hum- cancelling.”
PRS uses a 2.2k ohm resistor on the neck pickup and a 8.8k ohm resistor on the bridge pickup.
Alternately, the late Brit luthier Sid Poole showed us a good one, using a 4.7k ohm variable resistor (sub-miniature fully enclosed carbon preset potentiometers from Maplins, 49p each) mounted onto the control cavity backplate. This enables you to dial in the amount of the ‘dumped’ coil you want to hear.