just a quick one
if you connect red wire to a permanent live on ignition barrel, should be thick red, and other wire to switch live, ie wire that goes live when ignition is on probably yellow, then your LED will light up or flash only when you turn off the ignition, this way it wont be on all the time, example when your driving at night flashing led can be distracting.

this works because when ign is off, switch live is earthed and when ign is on wire becomes live and LED doesnt have a live and earth so doesnt flash.
sorry didnt turn out to be so quick, hope this helps