I have a non factory tach in my Ecodiesel which I conjured up about 3 years ago. link
http://www.vwdiesel.net/forum/index.php?topic=20437.0Anyway I started out trying to install a Peugeot tach, then a Mercedes tach, and finally settled on modifying a gasser VW MK II tach and fitting an inductive pickup from a gasser distributor and adding 2 magnet triggers on the crankshaft harmonic balancer. It has worked perfectly since until about a month ago when some road debris knocked the inductive pickup to pieces. I didn't have another distributor pickup and didn't even know what car it came from (it was from my junk pile). Just so happens I have an inductive pickup from a Mercedes tach and made a bracket for it and installed it yesterday and my tach is working again! This time I mounted it higher up behind the harmonic balancer more protected from flying road junk. I also installed the belt shroud so hopefully this won't happen again.
my pickup DOES NOT drive my stock tach..
if you took the sensor out of a VW dizzy, then it was a HALL EFFECT SENSOR..
magnetic pickup makes its own power, hall effect needs power..