I was designing this and ran into one already on the market. The parts would cost me more than buying this so I bought it. It's the latest idea in getting the attention of dizzy drivers behind you. Here's a Link to the site that sells and explains the technology. http://kahtec.com/smart_stop.htm
I got the one with the delay. It flashes the third light 6 times the first time you apply the brakes then stays lit solid. It does not flash them again unless you leave your foot off the brakes for 8 seconds. Then it again will flash them when you apply the brakes again.

I also have a DIY in a PDF that you can download to make things easier when installing.

http://www.filefactory.com/file/b1b3..._Light_DIY.pdf

I also put in a switch for my hatch light so that I can turn off the light while I have the hatch open for long periods.