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So I'm awaiting to wire in one or two relays so that a circuit is not powered until a push button is pressed. Then the circuit remains powered until total power is turned off. I've been trying to figure out how.

This is to put in a kill switch into a car (factory starter button). Want to disable the clutch switch until the button is pressed but allowing the clutch switch to remain operational while the car is turned on.

Can you guys help?


marked as duplicate by DoxyLover, laptop2d, JRE, Finbarr, Sparky256 Jan 2 at 22:36

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  • \$\begingroup\$ "Self latching relay circuit" is what you want. \$\endgroup\$ – Passerby Dec 24 '18 at 19:01
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    \$\begingroup\$ electronics.stackexchange.com/questions/66469/… \$\endgroup\$ – Passerby Dec 24 '18 at 19:03
  • \$\begingroup\$ @Passerby -- more commonly called a "stick relay" in fields where relays reign supreme \$\endgroup\$ – ThreePhaseEel Dec 25 '18 at 2:55
  • \$\begingroup\$ So what I've come up with so far is using 2 standard 4 pin automotive relays (no relays). When i press a momentary switch it energises the first relay. When it switches on, it keeps itself energised. This will also then energise the second relay acting as a switch. This will then allow the fuel pump, coil pack or clutch switch to activate. When car switches off, then the relays reset until the momentary button is pressed again. \$\endgroup\$ – Patrick Stuart Dec 25 '18 at 21:45
  • \$\begingroup\$ I've uploaded a very quick schematic of roughly what i mean - hopefully its about right. imgur.com/a/4znPztL \$\endgroup\$ – Patrick Stuart Dec 25 '18 at 21:51

Here's how to wire up a "self-latching relay" for your clutch switch. Choose a relay with 2 sets of contacts called a DPDT (double pole double throw) relay. Each set of contacts has a C (common) terminal, an NO (normally open) terminal, and an NC (normally closed) terminal. One set does the self-latching by feeding the coil hot input through the NO and the C terminals. The relay won't operate until those 2 terminals are momentarily jumped by the "kill" enable switch. Then the relay stays on, and only turns off when coil input power is removed. That is the "kill/enable" part of the circuit.
The other set of contacts control whatever you need controlled by this self-latching relay. To be even more effective, use 2 momentary switches near each other (one hand operation) or far apart (two hand operation. Both buttons must be pressed at the same time.


simulate this circuit – Schematic created using CircuitLab
To use this circuit: 1> turn on ignition. 2> press button(s). 3> relay is now latched on. 4> use clutch/starter circuit to start car normally. 5> when IGN is turned OFF, the relay unlatches.

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    \$\begingroup\$ This answer would be greatly improved if you af a schematic using the circuit tool. \$\endgroup\$ – Passerby Dec 25 '18 at 3:14
  • \$\begingroup\$ How do I access the circuit tool? \$\endgroup\$ – John Canon Dec 25 '18 at 4:33
  • \$\begingroup\$ I will post my jpeg drawing soon, then I will learn the circuit tool. Hang in there. \$\endgroup\$ – John Canon Dec 25 '18 at 4:41
  • \$\begingroup\$ Edit your post on a computer, one of the icons is circuit lab and it's fairly easy to use. \$\endgroup\$ – Passerby Dec 25 '18 at 5:32
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    \$\begingroup\$ +1. Good to see you promptly learn of and use schematic editor. | IF the SW1 (& SW2 if equipped) button(s) are able to handle the load briefly then you can use a SPST relay. (You know that but the OP may find it useful to know). \$\endgroup\$ – Russell McMahon Dec 25 '18 at 9:42

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