QuestionHow can I wire a car “push to start” button to a PC?

MikeinMD20878

My son found a tiktok video showing how to wire a car push to start button to his PC. I've been trying to help him, but the instructions haven't been very clear.

Here is the wiring diagram: View: https://imgur.com/XuQmszi

I soldered blue and black to an extension cable and discovered that connecting blue to PLED- and black to PLED+ causes the LED to light when the PC is on, the opposite of what I expected.

However, a continuity test determined that red/blue makes the power switch connection. So, how do I get the switch to power on the PC and light the LED at the same time when it appears that, according to the diagram, my split is coming off of the black wire (since my blue goes to PLED- )?

This is the button we bought.

Thanks.

punkncat

Splendid
All you need to start the PC is a momentary switch. If you have a meter or something that tests continuity, find out which two wires close as you press the button and verify they re-open the contact when you release.

As to powering the button, are you sure that it isn't looking for a 12V signal?

4745454b

4745454b

Titan
Moderator
I soldered blue and black to an extension cable and discovered that connecting blue to PLED- and black to PLED+
But that's not what the pictures shows. What happens when you wire it like your supposed to?

Titan
It depends on the switch. That picture could be correct for a Toyota but incorrect for a GM which switches ground, not hots.

So can't go by the picture as Gospel.

Need a multimeter. Figure out on the mobo exactly whether the 'power' and 'button' are hot, switched hot or ground.

On the switch, figure out which is common, is it a common ground or common hot. If common hot, then led- will be one wire, power will be common, button the other. If common ground, then led+ will be one wire, power the other and button common

CountMike

Titan
But that's not what the pictures shows. What happens when you wire it like your supposed to?
Looks like there's a light (bulb or LED) in that Start button. Wires Black which is negative and Green positive for light and on MBs it is on when PC is powered.
Red and black are momentary normally open switch and when button is pressed it connects negative and Start pins on MB and that turns PC on or off if it's already running, just like start button on "normal" PC case does.
In a car, Start button actually starts up it's computer and it in turn starts engine, so it's just about same thing.
Only problem could be with light in the button, PCs send 3-5v for light and cars are on 12v.
Switches and light bulbs don't care about polarity but LEDs do.

Titan
5v to a 12v led isn't a problem. It'll just be dimmer as the integrated resistor or resistance of the led in general will create less amperage draw.

It's 12v to a 5v led where issues happen as the amperage draw is just over double unless you add an additional resistor to soak up the voltage, typically @ 330ohm is about 7v worth.

MikeinMD20878

All you need to start the PC is a momentary switch. If you have a meter or something that tests continuity, find out which two wires close as you press the button and verify they re-open the contact when you release.

As to powering the button, are you sure that it isn't looking for a 12V signal?
My multimeter beeps when I press the button, so I think I have the correct two wires.

I'm not positive about powering the button, just that testing with a 9V battery lit the button with black to negative and blue to positive. That's why I was surprised to find that when the PC is on, blue to negative and black to positive powered the light.

MikeinMD20878

But that's not what the pictures shows. What happens when you wire it like your supposed to?
Nothing. I wanted to test it in steps first. If I connect blue to - and black to +, nothing happens.

MikeinMD20878

It depends on the switch. That picture could be correct for a Toyota but incorrect for a GM which switches ground, not hots.

So can't go by the picture as Gospel.

Need a multimeter. Figure out on the mobo exactly whether the 'power' and 'button' are hot, switched hot or ground.

On the switch, figure out which is common, is it a common ground or common hot. If common hot, then led- will be one wire, power will be common, button the other. If common ground, then led+ will be one wire, power the other and button common
Here are the motherboard and switch wiring diagrams.

How do I determine which is common and which is ground?

MikeinMD20878

Yes, but he's a 15 year-old kid and he's obsessed with doing this now. We got the power connection to work initially.

ohio_buckeye

Splendid
Ah. If you decide to go the other route, search eBay for pc power switch. All types off these kinds of things on there apparently.

Titan
You have a 9v battery. Touch one wire to + and one to -. Use the multimeter to check the polarity of the 3rd wire. Do you get 9v+ or 9v- or 0v when touching one then the other battery terminals. Might need to test for button on too.

If black is - and blue + lights the led, I'd assume black is common ground, and goes to power-, red to power+. Or blue is common+, black to led- and red to power -. It can be wired multiple ways depending on exactly how the switch is setup, which is common, whether that common is a ground or power.

It can be a pain, quite frustrating since the switch almost never comes with consise illustrations, it doesn't have to to be a replacement in a car.

Ralston18

Titan
Moderator
"Yes, but he's a 15 year-old kid and he's obsessed with doing this now. We got the power connection to work initially. "

Understood.

Ask him how obsessed he is with sparks, flames, smoke in his PC if the wiring, etc, is not done correctly. Might even work at first and then go "poof" later.

You can turn this all into multiple lessons.