I would buy the original alarm switch and wire it up behind the dash to illuminate the LED
Me too as most peolple know what they look like anyway. Anything else may look trashy
Look for a standard RED flashing LED, as that is what the alarm guys use mostly, they seldom use green, blue or any other colours, so if you want it to look like an alarm, keep it simple.
You can buy a 12V flashing LED for a couple of quid, and make sure that you fit it somewhere near the stereo or dash panel, as these are generally the first places people glance inside, and also where the alarms fitters choose to locate them.
http://cgi.ebay.co.uk/Car-Caravan-Marine-Alarm-Flashing-Blinking-LED-12v-RED-/270546487264?cmd=ViewItem&pt=UK_Campervan_Caravan_Accessories&hash=item3efdd3c7e0Your LED will probably have a red and a black wire.
Connect the red wire to a supply that is permanently live, and connect the black wire to a supply that is only live when the ignition is switched on, and that way when the keys are taken out the LED will start to flash.
Ignition and permanent feeds can be found at the rear of the stereo amongst other places
Hope this helps
