another tach question

[shegel]

when i turn the headlights on in my newly aquired 86 jetta turbodiesel the tach signal dies. this also happens when i hit the high beam switch when the headlights are not on. it goes from 1000 to zero like its grounding or somthing. ... I am pretty mechanicly inclined to begin with and can troubleshoot most things but am unsure what to start with on this problem. i would pully meter out but i have to go to work soon  

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thanks,
steve

[JerryGTD]

Sounds like a loose alternator belt to me.

[shegel]

belts tight.