Warning Light???

Post by **jane_b** » Sun Apr 27, 2003 11:29 pm

I seem to recall fitting a warning LED some years ago that operated when the ignition was turned off - a sort of 'this car is alarmed' thing. I know that the LED was a bog standard one but can't remember exactly how it was wired.
I think that the positive was wired to a permanent 12v supply and the negative went to the switched side of the ignition. The effect was that when the ignition was turned on the LED wasn't, when the ignition was turned off the LED came on.
Is this the correct way of wiring an LED to do this or am I totally mistaken??? I need to know so that I can do the same again.

Post by **Cam** » Mon Apr 28, 2003 2:20 pm

That way of wiring should not work on a Moggy as there is no earth going to the ignition switch. You can do it quite easily if you use a small relay (normally closed - or single pole double throw (SPDT)).

If you connect the coil of the relay between earth and the ignition switched live, and then use the normally closed relay contacts to switch the live to the LED and earth the LED normally.

Post by **Gareth** » Mon Apr 28, 2003 2:36 pm

To be really unobtrusive, maybe you could wire it so it made the ignition light flash... although that would draw more current, and I don't know what effect it would have on the charging system, if any...

Something to ponder on, perhaps?

Post by **Cam** » Mon Apr 28, 2003 3:16 pm

I don't know what effect it would have on the charging system, if any...

None, if you switched it from the charging circuit to a constant live through the relay, but you are right, it would draw a lot more current.