Help with incredibly simple question on a switch

Thread Starter


Joined Sep 2, 2019
I'm almost embarrassed to post this one... it's so simple but I just want to be sure I have it right. I have attached a schematic. This is for an automotive application. I have a ground connection for pin 1. I want to power a device using the Remote (switched power)… and the mfr. recommends fusing it at 1A. The switch can easily accommodate that load, so how do I wire this? I always get these simple ones confused. I think more like a computer than like an electrician. Is this switch normally open? do I hook my positive source to pin3 and my output to the device to pin 2 then ground on pin 1, or do I connect the source to 1 and the load to 3, and if so what do I connect to 2? Thanks for any help.



Joined Jan 17, 2007
The ground pin #1 is there to light up a led lamp embedded in the switch, and it's not strictly necessary for it to function.
Pin #3 is connected to your power source, i.e. the car's battery or fuse box.
Pin #2 is connected to whatever device you want to switch on and off.

The normally open/closed state of the switch depends on if it's of the momentary action of not. That is, depends on it having a spring that will return it to its original position if you activate it with your hand, and then release it. If that is the case, then it apparently is of the normally open type, according to the diagram you've posted.
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Joined Mar 11, 2019
Well the schematic makes it look like ON means open. Easiest thing to do is check it with a dmm to be sure which is which if the switched is labeled.
The rest looks to me like you could go either way:

LED would alway be on when fuse 1A was on.
PIN1 : ground
PIN2: fused at 1A
PIN3: To your load

LED only on when switch is active:
PIN1 : ground
PIN2: To your load
PIN3: fused at 1A
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Joined Sep 24, 2015
@cmartinez Not sure I followed your pin numbering. I think you might have cited a pin number out of order.

Pin 3 is connected to your power source (car battery, either always hot or a key switched circuit)
Pin 2 is connected to the device you want to control.
Pin 1 is solely for lighting up the LED. Grounding pin 1 will light the LED when the switch is in the on position.

You asked if this is a "Normally Open" switch. For any switch to be "Normally Open" it must have a resting state in which the contact(s) is(are) open and only closed when the switch is actively being held in it's NOT Normal position. That's typical of a spring loaded switch. What you have simply is a single pole single throw (SPST) switch. It's open when you switch it off and closed when you switch it on. When it is open (off) the LED does not light, and your load (whatever it is you're powering) is off.

If you need a diagram just ask. It's easy enough to draw out, and I'd be happy to make such a drawing.


Joined Sep 24, 2015
After looking closer at the diagram I see that if you hook battery power to pin 2 the LED will be on whenever there's power. You CAN hook the load to pin 3 if you want.

So there are two different configurations possible. Here's a drawing: (below)

Configuration A: The LED only lights when you turn the switch ON
Configuration B: The LED lights whenever power is available - regardless of switch position.

In "B", if battery power is available only when the key is on then B is acceptable. If power is not key switched, the LED will be on at all times regardless of key position, and you will drain the car battery.

Battrey n switch.png


Joined Sep 24, 2015
As far as the illustration goes - the pin out (numbers) are shown in the Thread Starter's picture. The LED is shown there as well. And the switch is a SPST switch (Single Pole, Single Throw). Notice I didn't draw the toggle either. No need to. The focus is how to wire it.

Technically speaking; pin 1 is the cathode of the LED. There MUST be a limiting resistor in there as well, but none of the illustrations show such. It's just assumed that this LED is a 12 volt systems LED. There are two ways the switch contacts can be hooked up - power in at either pins 2 or 3 and power out at the remaining pin. If power in at 2 then power out at 3. Or vice versa, in at 3, out at 2. How are you confused? Did the TS say it was confusing?


Joined Jan 21, 2019
my assumption is that if the LED is in an automotive 12V switch, it's already limited... I have 24V industrial switches that have the same thing... it's already done for you.


Joined Sep 24, 2015
think too much
What's too much about two ways to hook up the switch? Ether you apply the source to pin 2 or 3 and the other pin, 3 or 2 is the power out. Pin 1 is the LED ground. If you apply constant power at pin 2 the LED is constantly lit. If you apply constant power to pin 3 then the LED is only lit when the switch is closed.

And just to be clear: Thinking is NOT my strong point! So when possible I try to avoid thinking. Simplistic explanations are clear for me. It's how I accomplish the task of thinking. That's why I stay away from complex circuits and avoid commenting on things I know I don't know.


Joined Sep 24, 2015
Yes, it is rather clear. However, the TS was not sure and wanted to make sure he had a full understanding of how to use the switch. Hey! We all had our first times with new concepts in electronics. While many of us find this of the utmost basic, it IS what the TS wanted to know.