[Vwdiesel] 85 Jetta turbo diesel GL tachometer going whacky

[W Davis]

Awhile ago, I had a sudden problem..driving home from work;
all of a sudden, the alt light began to glow, dash lights went out, and the tach 
started going all over the place.

Long story short, I pulled the voltage regulator from the alternator, and simple 
visual
inspection showed it was bad...replaced the v-reg with a new one I had, and all 
was
well again, except I still have intermittent "whacky tach syndrome".

1-  from what source does the tachometer sense what it's reading?..is it the 
alternator?

2-  what might be the problem..the tach itself,, or the source from which it 
gets its' info?

Many thanks,

William in Fla

1985 Jetta GL turbo diesel, my daily driver,
 running fine otherwise.