Why third input on an LED switch?

[mattonthesea]

I'm just about to wire in a 12v switch with an LED indicator light on it. It has three terminals: +ve, -ve and one for the LED. This one says wire to earth; as it's for a car I imagine that this means the negative so can I just join these two? (or are cars +ve earth these days?)

Is this terminal to stop the entire current flowing through the LED?

Confused of Bristol

 

[MoodySabre]

A switch just switches the live (positive). To make the light come on you need an earth (negative) too.

 

[VicS]

I'm just about to wire in a 12v switch with an LED indicator light on it. It has three terminals: +ve, -ve and one for the LED. This one says wire to earth; as it's for a car I imagine that this means the negative so can I just join these two? (or are cars +ve earth these days?)

Is this terminal to stop the entire current flowing through the LED?

Confused of Bristol

The third connection is a negative connection for the LED

The positive supply from the battery goes to one terminal. Probably marked power or +
A negative supply goes the terminal which is probably marked ground or - The terminal may be a different colour
The load connects to the remaining terminal possibly marked acc



Make sure you have correctly identified the terminals before you connect it or you may short out the power supply. Check it out with your multimeter if necessary..

 

[PaulRainbow]

I'm just about to wire in a 12v switch with an LED indicator light on it. It has three terminals: +ve, -ve and one for the LED. This one says wire to earth; as it's for a car I imagine that this means the negative so can I just join these two? (or are cars +ve earth these days?)

Is this terminal to stop the entire current flowing through the LED?

Confused of Bristol

I think the labelling on the switch is what's causing the confusion Matt. I've seen this before with cheap switches where +VE goes to 12V positive. -VE goes to the load and the last one goes to 12V negative. Double check by connecting a multimeter, set to buzzer, continuity, between the +VE and -VE terminal. Operate the switch and the buzzer should go on/off.

 

[PaulRainbow]

The third connection is a negative connection for the LED

The positive supply from the battery goes to one terminal. Probably marked power or +
A negative supply goes the terminal which is probably marked ground or - The terminal may be a different colour
The load connects to the remaining terminal possibly marked acc

Following this advice will most likely destroy the switch, were it not for the last bit of advice.

If you re-read post #1 you will see that it's impossible for anything to work as you described the connections, he'd have a negative to the LED terminal (which would be correct) and a negative to the -VE terminal (which you'd expect to be correct, but i'm fairly sure it's mislabelled and should really be the load terminal).

Make sure you have correctly identified the terminals before you connect it or you may short out the power supply. Check it out with your multimeter if necessary..

 

[mattonthesea]

So obvious when you draw it!

Working fridge and LED. But so happy to do this that I forgot to put a fuse in-line. Doh Next time.

Thanks everyone

M