coil #1 is grounded on both sides effectively eliminating it from the circuit leaving coil #2 to operate by itself! Have a look at the schematic pics. So, if you connect a wire to the place where the 2 coils connect together and then connect that new wire to ground.
Since the 2 coils of the humbucker are wired in series, that means that one side of each coil is connected together, the other wire on coil #1 goes to ground, and the other wire on coil #2 is the output signal. The more subtle, but what we're concerned with here, is the different tonal characteristics. The most noticeable is that the output is higher. There are a couple of side effects of using dual coils in this way that are not necessarily undesirable. This helps to greatly reduce the hum you hear when using single coils at higher gain levels.
BOSS SD 1 SINGLE COIL VS HUMBUCKER SERIES
Since they are in series and of opposite polarity or phase, they reduce noise caused by interference by common-mode rejection. The trick is that the magnetic pole pieces in one coil are oriented with the N magnetic pole facing the strings and the other coil with the S magnetic pole facing the strings making the 2 coils magnetically opposite. Ok, humbucker pickups are, if you didn't know, 2 single coil pickups wired in series. The push/pull volume POT is the way to go to keep this mod reversible if you have an expensive or vintage instrument and still want to make changes to it. I had to cut a hole to fit the switch, but I wasn't modding a vintage '56 les paul goldtop or anything! I got this guitar at my local pawn shop for $60! So, take that into consideration when choosing to perform ANY modification. In my case, there wasn't much room and I didn't have a suitable push/pull POT in my collection, so I added a discrete sliding toggle switch between my existing volume/tone knobs. If you intend to blend the two coils you will need a push/pull pot installed in addition to whatever knobs you already have, so make sure you have the necessary space for whatever new components you'll be adding before you blow the money on parts. You can get a push/pull type potentiometer/switch to replace your volume POT, or you may have to cut a hole in the pick guard to mount a toggle switch. If all you want is to turn your humbuckers into single coils you can pull that off in about 20 minutes with nothing more than a small piece of wire! Adding a switch will be more challenging mostly because you need to find a place to put it.
BOSS SD 1 SINGLE COIL VS HUMBUCKER MOD
In it's simplest form this mod is very easy. This would take advantage of the humbuckers hum cancelling properties as much or as little as required for the current volume/gain settings. Another possibility, would be to use the pickup as "mostly" single coil to get that single coil tone that is often desired, but use the blend control to dial out some of the characteristic hum at higher gain levels. Using a control scheme like this on all of the available pickups would create many tonal variations that can be easily tweaked during a performance. For example, It is possible to create a single pickup that operates as both a single coil AND humbucker with a control to blend how much of each type of sound is routed through the guitar's controls to the amp. In this instructable, I'll show how I installed a switch to make both of the humbuckers on my guitar operate as single coils at the same time, but I'll also describe some other options in detail. This will give you the tone and dynamics of a single coil (and the hum too) without buying new pickups AND you can go back to humbucker configuration with the flick of a switch! There are a ton of possibilities here to configure different tones on your guitar if you care to experiment. If you have a guitar with dual-coil pickups, or humbuckers, you can easily modify the wiring to allow you to use just one of the coils on each pickup instead of both coils.