I have a 2 pin foot pedal that is an NO switch. When i press the pedal down, the circuit closes. I basically need it the other way round. This will be used to operate a switch on a DC motor speed controller which will shut it off. Basically a foot brake. The way the motor controller is currently setup is the power switch is a potentiometer with a switch. when the potentiometer is in the NO position, the controller is off and visa versa.

I would like to connect the foot pedal instead of the potentiometer as it'll be used in a little car but currently i need to keep my foot on the brake pedal for the controller to stay on!

The way I'm thinking of wiring it is via a relay. 12v battery to pedal pin 1, pedal pin 2 to relay pin 86, relay pin 85 to ground, relay pin 87a to dc controller pin 1 and dc controller pin 2 to ground. does that sound right?

I've tested it with a multimeter and the results seem correct where the circuit is normally closed but once i click on the pedal, the circuit opens. I just want to check before breaking anything.

thanks for any feedback.

EDIT: this is a crude picture of what I'm trying to do. Not sure if i need to use pin 30 though?

foot pedal relay setup

EDIT 2: enter image description here

  • \$\begingroup\$ Please include a block diagram/flow chart. It's not clear what do you want. If you have a pedal, then where is the necessity of that switch. \$\endgroup\$
    – Sadat Rafi
    Apr 18, 2020 at 19:27
  • \$\begingroup\$ you connected only one relay contact .... look at this duckduckgo.com/?q=relay+86+87+87a&iax=images&ia=images \$\endgroup\$
    – jsotola
    Apr 18, 2020 at 20:43
  • \$\begingroup\$ that doesn't help me. i just need clarification on how's best to wire up the relay to essentially invert the pedal switch. do i power pin 30 from the battery as well? \$\endgroup\$
    – Sal
    Apr 18, 2020 at 21:08

2 Answers 2


Your diagram will work, but you will need to connect pin 30 to the other half of what you want to be normally closed

  • \$\begingroup\$ thanks for your answer. can you clarify pin 30....my thinking is i don't need any power as such, just continuity between the pin 1 + 2 of the controller switch (currently the potentiometer. this is what is confusing me a little. maybe swapping 87a and 30 and then putting pin 2 of the controller switch to 87a? i've added a 2nd diagram for clarity of my comment \$\endgroup\$
    – Sal
    Apr 18, 2020 at 21:52
  • \$\begingroup\$ 85 and 86 are power to the relay, 30 87 and 87a are the switch contacts, there are no internal connections between these 2 groups of pins, as such if 87a is meant to be held with a normally closed contact to battery, you will need to supply that to pin 30 \$\endgroup\$
    – Reroute
    Apr 18, 2020 at 21:55
  • \$\begingroup\$ my 2nd diagram should work then? pin 30 is always connected to 87a until there is power to the relay, in which case 30 and 87 will then be connected. I'm not sure why i would need the battery connected to pin 30 though? \$\endgroup\$
    – Sal
    Apr 18, 2020 at 22:08
  • \$\begingroup\$ That is correct, sorry I was not fully clear what that contact pair was doing \$\endgroup\$
    – Reroute
    Apr 18, 2020 at 22:10
  • \$\begingroup\$ thanks man, much appreciated :) \$\endgroup\$
    – Sal
    Apr 18, 2020 at 22:15

Here's the relay schematic.

enter image description here

The coil (terminals 85 & 86) is to be energised by your foot pedal switch.

The NC contact (terminals 30 & 87a) is what you need to invert the foot pedal switch function.

When the coil is energised, the NC contact (terminals 30 & 87a) opens and the NO contact (terminals 30 & 87) closes.


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