I made one out of an Arduino. Overkill, I know, but it cost under £10 in parts, anyway, and it's infinitely tuneable ;-).
https://www.youtube.com/watch?v=E3j_aek5Y-0
The outputs are just LEDs connected to the output pins with 560 Ohm resistors.
The input is a stabilizer with a 1K resistor and a 4.7V zener. I can sketch the schematic if anyone's interested.
For the "production" version I used a $10 Arduino Pro Mini. Here are some pics of the final product without the 3d printed box it's in now:
http://imgur.com/a/IHBOv
Also, I added a 7805 stabilizer for power feed, as Arduino Pro Mini is rated only up to 12V, and in the car it can get more than that.
The code is available here:
https://github.com/alga/shiftlight
The circuit used to work perfectly with Ford's ECU, but after the MS3 install it catches some interference and blinks sometimes. I can't get around to hanging a low-pass filter capacitor on the input.