I just put one on my Bonneville. Somewhere in these forums are some directions that I copied and downloaded the pictures to follow... do a searcha and you should come up with it.
I got a mini tach off of Ebay for $20US and wired it up per the directions - works perfectly right off the bat.
This is what you should look for. The one I bought was used, but works great. I think any 12volt 8000 rpm tach would do... Do some searching on Ebay for "mini tach" and you'll find a bunch.
This site has the pictures I followed:
http://oldsport.home.comcast.net/tach/
It took some cajones to cut that first wire, but the directions are right on the money. If you need any help, feel free to ask.
[ This message was edited by: psasak on 2006-10-30 15:59 ]