If you are really into guitar modding, there is no way around learning how switches work. So this month let’s explore the basics.

Two types of switches are commonly used for guitar mods. One is a potentiometer with a switch—a push/pull, push/ push, or the Fender S-1—and the other is a common toggle, which is available in different sizes, shapes, and configurations. When adding a switch to a passive circuit, you don’t have to worry about voltage and power ratings—all that matters is that switch will fit your guitar!

Though switches come in various configurations, they all have a single purpose—to turn a signal on or off. Many variations are available, but we’ll concentrate on the four most common guitar switches: SPST on/off, SPDT on/on, DPDT on/on, and DPDT on/on/on.

The first two letters of these names indicate the number ofpoles, while the last two letters are the number ofthrows. So a SPST (aka 1PST or 1P1T) means single-pole/single-throw, a SPDT (1PDT or 1P2T) means single-pole/double-throw, and DPDT (2PDT or 2P2T) means double-pole/double-throw. There are many more configurations, including 3PDT devices used for true-bypass switching in effects, and Fender’s 4PDT S-1 switch. Found on push/pull or push/push pots, the DPDT on/on switch is by far the most common, and mini toggles are available in an endless number of variations.

Let’s take a closer look at what’s known as theswitching matrix. A switch’s poles are like separate channels that aren’t connected until you add a jumper wire between them. A SPST or SPDT switch has only one of these channels, while a DPDT switch has two. Likewise, 3PDT and 4PDT switches have three and four channels, respectively. A switch’s throws are simply the different sides of a switch. For example, a DPDT on/on switch has two channels (poles) with three lugs on each channel. Engaging the switch turns on one side or the other. When one signal is turned on, the other is turned off.

An SPST switch has only one channel (pole) with two lugs. It’s the archetypal on/off switch for simple projects like replacing a 5-way switch with three on/off switches. In one switching position, the two lugs are connected, while in the other they’re disconnected. Below is a visual representation of the SPST switch.

In one position, lug A and lug B are not connected (that is, the circuit is open). In the other, both lugs are connected (the circuit is closed). To use our seven-sound mod as an example: In one switching position, both lugs are not connected, so the neck pickup connected to the switch is not engaged. In the other position, both lugs are connected and the neck pickup is engaged.

This is a great opportunity to start working with a digital multimeter (DMM). Track down an inexpensive DMM and make sure it has a continuity function, preferably with an audible connection indicator. You can then trace how switches work by connecting the individual lugs to your DMM and seeing which are connected, and then switching to the other position and taking the same measurement again. The beep that sounds when you’ve made a connection is a great help when you’re taking these measurements.

A SPDT (1PDT or 1P2T) on/on switch also has only one channel (pole), but offers three lugs instead of two. This switch also works for the seven-sound mod (if you leave one lug unconnected) or for the cap-switching mod. Below you’ll see what’s going on in this type of switch.

In one position, lugs A and B are connected (this is throw 1), while in the other position lugs B and C are connected (throw 2). So lug B is the common output of this switch, while lugs A and C are inputs.

A DPDT (2PDT or 2P2T) on/on switch has two channels (poles), each having three lugs. This is like having two SPDT switches in one. It’s the standard configuration for most push/ pull or push/push pots, and you can use it for almost all mods, including the seven-sound mod (if you leave one pole unconnected), coil-splitting a humbucker, out-of-phase mods (by adding some jumper wires from pole 1 to pole 2), a direct-through mod, and countless others. Let’s see what’s going on here.

In one switching position, lugs B and C of pole 1 and lugs E and F of pole 2 are connected (throw 1). In the other position, lugs A and B of pole 1 and D and E of pole 2 are connected (throw 2). It’s exactly like a SPDT switch, but with two poles instead of one.

Finally, we come to a very special but important type of switch: the DPDT (2PDT or 2P2T) on/on/on. Larry DiMarzio made this switch famous in the ’80s, and this is the device to use when you have a four-conductor humbucker and want to take full advantage of all its wiring possibilities.

It’s still a 2PDT switch with two channels (poles) sporting three lugs each, but in comparison to a DPDT on/on switch with only two switching positions, the DPDT on/on/ on switch has three positions. This is often called a “centeron” switch, because it has a third position in the middle between the common left and right positions.

Although the DPDT on/ on/on switch has the same number of poles and lugs as our previous DPDT on/on switch (which means the illustrations for these switches look identical), this version has an additional switch position.

In switching position 1 (left throw), lugs B and C of pole 1 and lugs E and F of pole 2 are connected. In position 2 (center throw), lugs A and B of pole 1 and lugs E and F of pole 2 are connected. Finally, in position 3 (right throw), lugs A and B of pole 1 and lugs D and E of pole 2 are connected.

This switch facilitates three sounds from a four-conductor humbucker: both coils in series (standard humbucking mode), both coils in parallel (sounds similar to a single-coil, but in a hum-cancelling configuration), and a true single-coil mode.

All right—that’s it. I know this is very dry, but it’s worth investing some hours to understand switching basics.

See you next month—and keep on modding!

Dirk Wackerlives in Germany and is fascinated by anything related to old Fender guitars and amps. He plays country, rockabilly, and surf music in two bands, works regularly as a session musician for a local studio, and writes for several guitar mags. He’s also a hardcore guitar and amp DIY-er who runs an extensive website—singlecoil.com—on the subject.