How much current draw? If low, might consider just taping into the lights (headlight/running), since most roadkills happen at night, or poor light, you would most likely have your lights on anyway. My 2000 Grand Prix truns the lights on automatic, when the car is running. During the daytime, you should be watching, and able to see things in plenty of time to avoid hitting them.
If/when the Obama/Gore Climate Control bill ever passes, most of the older vehicles won't pass the requirement, although I'm sure there will be something that will allow people to keep driving them, least for a while. Think most newer vehicles have the lights on these days.
How much range does this have, will it make much difference at 80 MPH (or faster)? I've got sort of a lead-foot when traffic is light or non-existent, being fewer obstructions, and unlikely a cop is hiding behind the bushes, hunting for speeders. If there is one, he knows I'll be miles away, before he can zip up...