I've been in the process of replacing the ordinary "mint green" lights on the interior of my Intrepid to some red LED's I have laying around (I have 50 blue ones on the way which I think I'll go with).
I've wired up and installed them on my shifter bezel and climate control panel (basic three knob unit). In the house, it all runs perfect off a 9V battery. Take it outside, plug it in, turn on the car, they come on, and suddenly die out never to come on again.
I've NEVER burnt out LED's in my life running them on 12V connections, in fact, these LED's were pulled from a few old Intrepid Clusters that I've been experimenting with.
Any advice boys?