That looks pretty neat! I use a Stack fuel gauge myself to match the other Stack gauges I have in my dash - it's programmable so that you can get the full and empty reading right.
I take it you have measured resistance across the 2 fuel gauge wires at full and empty to get the full sweep?
Have a look a this for help on wiring - page 12, wires B4 and B5 are to the fuel sender:
http://luuk.xs4all.nl/bmwboeken/bmw%203 ... agrams.pdf
Bottom line is that you need something programmable to hook into the standard sensor...
Good luck!
