Originally Posted by Red.
If you have a tripod and (ideally) a shutter remote of some variety, you could just dial your camera over to M, keep your ISO down around 200-ish, open up your shutter, walk over to the cars - either have the driver's side window already rolled down or open the door - turn the lights on for a quick flash, turn them off, close the door, walk over to the next car, repeat.
If you don't have a shutter remote you can just set your timer to 20 or 30 secs and be quick about moving from one car to the next. But, remotes can be had for cheap and they are so useful, both day and night. I highly recommend having one.
Anyway, that's just my method to my madness. Everyone figures something out. Part of why I do it this way is that I know I'm not going home to photoshop so everything I want in my photo pretty much has to be captured in-camera, in a single exposure. I'm sure that after some trial and error you'll sort something out that works for you.
Thanks Red. I'll give this a try too and see what I can come up with. Unfortunately, my 1000D won't work with a wireless remote. So it looks like I'll be running around like an idiot from car to car lol. Or I'll just make people sit in the cars to turn the lights on.