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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.

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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).

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  • \$\begingroup\$ It's guesswork at best. \$\endgroup\$
    – Andy aka
    Commented May 29, 2020 at 13:33

2 Answers 2

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schematic

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.

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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.

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  • \$\begingroup\$ Thanks very much for your clear and thorough explanation. I've reconnected the wires in the way suggested, but it seems I've done something wrong because now the polarity switch acts as the on/off for the sustain and the footswitch doesn't appear to do anything. Before I go to rewire it, what could I have done to end up with the above result? \$\endgroup\$
    – aru
    Commented May 29, 2020 at 14:23
  • \$\begingroup\$ @aru That indicates either (1) the switch is not a standard DPDT, and you found two terminals that are permanently connected, (2) the foot switch is now broken, or (3) things are not quite as you described them. I suggest editing your question with a photo of the internals. Make sure it is well lit and in focus, and doesn't obscure any of the connections. \$\endgroup\$
    – Kevin Reid
    Commented May 29, 2020 at 15:00
  • \$\begingroup\$ @aru Also note that, as I mentioned, a multimeter can be used to figure out the switch behavior. It's just tedious because you need to measure every pair of terminals while pressing and not pressing the switch. \$\endgroup\$
    – Kevin Reid
    Commented May 29, 2020 at 15:01
  • \$\begingroup\$ I've added a few photos to my original post. I'll have a look for my digital multimeter, although I'm not sure if it has a continuity test mode. \$\endgroup\$
    – aru
    Commented May 29, 2020 at 16:08
  • \$\begingroup\$ @aru Your rewiring looks fine to me (assuming the three wires are all wired on one side (pole) of the switch, which isn't entirely clear). Time for troubleshooting. Find out if each switch is actually switching properly. \$\endgroup\$
    – Kevin Reid
    Commented May 29, 2020 at 20:30

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