Fixing the wiring on a keyboard sustain pedal

Question

I have a cheap keyboard sustain pedal of the basic on/off variety. When the footswitch is pressed down sustain is on, and off when it's released. There is also a polarity switch so that it can be used with different makes of keyboard.

I opened the pedal to apply some grease and when doing so managed to disconnect the wires from the footswitch. I don't know the correct way to reconnect these wires. I have a attached a quickly drawn diagram of how things look.

The smaller rectangle is the polarity switch, which has 3 prongs, and the larger rectangle is the footswitch, with 6 prongs.

I need to know what numbers on the footswitch do the blue, green and red wires connect to, and also if any of the prongs on the footswitch should be connected to each other.

PS. Here's a few more photos as requested. I changed the colours of the wires in my diagram for the sake of clarity (pink in diagram = white, blue = black, green = red, red = also red).

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Try this.

How it works:

• As shown the sustain switching is normally open. Pressing the pedal completes the circuit.
• Reversing the MODE switch will make the circuit normally closed. Pressing the pedal will open the circuit.

'C' indicates the common or centre pin on each switch. (You only need one side of a two-pole switch.) This is the quite similar in operation to a two-way stairs lighting circuit.

Answer 2

A 6-terminal two position switch is almost certainly a DPDT (double pole, double throw) switch. Such switches are so common that they are often used even when the application does not need two poles.

• Double pole means that the switch has two independent sets of contacts, so that it can change two circuits (or one circuit in two places) together.

  This is irrelevant here; there's only one circuit. You may be able to tell which pole was originally wired by looking for signs of wear, but it doesn't matter which one you use.

• Double throw means that the switch has two positions, and it closes contacts in both of those positions, rather than being entirely open in one of them.

  This is how the foot switch can work with the reversal switch. It's the same principle as a "three way" light switch setup where two switches can both turn the light on or off.

In a DPDT switch, you usually see a 2 by 3 array of terminals (as you have drawn). The two is the two poles, so there are two identical sets of three. Looking at the three, the center one is almost certainly the "common" terminal, which should go to the unswitched (red) wire in your cable. The switch connects that terminal to either of the other two in its two positions.

Connect red to the foot switch's middle terminal, and connect the two wires from the polarity switch to the outside two terminals. Either way will work; it only changes which way around the polarity switch works.

If you have a multimeter, you can use its continuity test mode to find out which way the switch works and wire it to work the way it used to. In fact, you can use the meter to learn everything I've told you, though with more time spent checking possibilities.