I had a quick pokey around and found a piece of kit made by a guy called George Graves from E30tech:
[youtube][/youtube]
Further nosing around found me this site:
http://www.scirocco.org/tech/misc/afgauge/af.html
So I've used the circuitry from the site and combined it inside an old hazard switch housing and guess what! It works! and it only cost a tenner in parts...bit of a tweak in brightness and it'll be perfect!

Just thought I'd share!












