In my car there is a switch to control traction control that's Normally Closed that I want to swap to Normally Open, however there is a problem. When the car is turned off and back on, the state resets to closed. I want to replace the switch but I also want to keep this feature.

Is there a momentary button operation switch that will toggle signal wire open/closed but will default to NO when power is lost?

  • \$\begingroup\$ Any electronically controlled button will do that (or a button latched by an electromagnet when pressed but I don't know if those exist). \$\endgroup\$
    – DKNguyen
    Commented May 29, 2020 at 19:34
  • 1
    \$\begingroup\$ you can wire the button to a relay that self-triggers to "latch" open until power is removed. Or use a triac instead of a relay, and trigger with the button. \$\endgroup\$
    – dandavis
    Commented May 29, 2020 at 19:39
  • \$\begingroup\$ @dandavis Note that if using a triac you may not be able to "unpress" the button without powering it down without additional measures (which would also be required to unpress electromagnetically latched button). It's one thing to make something volatile that just latches when pressed and stays that way until powered down. It is another thing to make it so you can also unlatch it while powered. \$\endgroup\$
    – DKNguyen
    Commented May 29, 2020 at 19:54
  • \$\begingroup\$ @DKNguyen: true, same for a self-latching relay. OP didn't mention "canceling" it, so I assumed it was ok. If that feature is needed, I don't see a way to avoid a 2nd button, unless we go to a simple MCU or clever multi-discrete solution; OP can look for a "soft latch circuit". \$\endgroup\$
    – dandavis
    Commented May 29, 2020 at 19:56
  • \$\begingroup\$ @dandavis I initially assumed it was okay too but then upon reading the question again, I think he may want the option to turn off traction control without shutting the car down. \$\endgroup\$
    – DKNguyen
    Commented May 29, 2020 at 19:57

1 Answer 1


Since I do not have reputation to comment, I am posting my answer here:

Look at question, where OP wants to do something similar with start&stop system. You can use the same circuit i drew in the answer.


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