I also have been adding Evan Designs police lights to a police car, for use in the "small town" area. This was surprisingly straightforward... The Crown Vic is well suited to this, even if it's a little tricky to get LEDs lined up perfectly and not drill all the way through the roof lights 
Here's the police car shell:
Here's the underside with the wires in place:
...and here's a close-up of the interior. I added some painted details to the interior while I was at it:
...and here it is mid-flash. Success:
I'll also try uploading a video:
