I'll be fitting the cathode to a permanent +ve, with the anode to the +ve that loses power to the radio when the key is removed. That means the -ve will be provided via the residual earth through the radio when the key is removed. Hopefully.

I wouldn't rely on that working, the chances are pretty slim. What I would do is connect a small relay (only needs to be able to switch about 50mA) to the switched 12V that goes on an off with the ignition, while the NC connection goes to permanent 12V. The common would then go to a resistor if the particular LED you have needs it (there are LED's that have flashing circuits and run direct off 12V) then to the LED and ground as per the attached schematic.

When the ignition is on, the relay pulls in, disconnecting the power to the LED. When off, the LED is powered.

[Rubix]

I think I'm going to have to find an online reader called "electronic circuit jargon and schematics for dummy's". I've found some great schematics for how to create these circuits, but buggered if I know what a "K1" is or a "CM1-P" :S

[YOSOYPEPO]

like this strobe lights?

http://www.dealextreme.com/details.dx/sku.15729

I think I'm going to have to find an online reader called "electronic circuit jargon and schematics for dummy's". I've found some great schematics for how to create these circuits, but buggered if I know what a "K1" is or a "CM1-P" :S

Ignore the desgination on the relay. I threw the circuit schematic together with the help of the Eagle schematic editor and just used one of their pre-canned components to illustrate the circuit.

[Rubix]

I think I'm going to have to find an online reader called "electronic circuit jargon and schematics for dummy's". I've found some great schematics for how to create these circuits, but buggered if I know what a "K1" is or a "CM1-P" :S

Ignore the desgination on the relay. I threw the circuit schematic together with the help of the Eagle schematic editor and just used one of their pre-canned components to illustrate the circuit.

still doesn't help me work out the other circuits I found - I found one specifically for creating alternating flashing leds.

[YOSOYPEPO]

are you going to try to do it?

I might.

I would put a single LED on the dashboard, probably near the radio. It would be a blue LED and I would try to locate the power line that is active once the alarm has been set, if possible.

Maybe something like this (eBay)



EDIT: I just bought that item.

Thanks YOSOYPEPO for showing how easy it is to do

heve you recived blue leds?

[Shambles]

heve you recived blue leds?

Yes a long time ago. I just haven't had the time to do anything with it yet.

[YOSOYPEPO]

heve you recived blue leds?

Yes a long time ago. I just haven't had the time to do anything with it yet.

ohhh i haven't recived yet. i think blue led may be missing :S

[Shambles]

heve you recived blue leds?

All fitted and working now - see this thread

How will this led work in the car, is it going to blink when the cars off, if so I hope you have better luck than me finding a 12V high current wire when the car's off 

Blinks at 2Hz when the key is removed. The two wires I chose were on the hazard warning light button. One is permanent +12v while the other drops to 0v when the key is out, rising to +12v when the aux key position is selected (meaning there is no potential across the LED, so it goes out)