Tach on my 94 is having problems

[2.slowjetta]

My tach randomly will jump around sporadically, and sometimes it will work prefectly.
I have a brand new alternator that I had to install becuase my last one wouldn't start to charge unless I hit the alternator with a screwdriver handle or something like that. The old one worked fine and gave a normal tach signal.
The new one also worked fine for a while then started doing this. I'm just wondering if I should be getting the alternator replaced under warrenty or should I be looking at the wiring?

Ideas, Comments, Past Experiences?

Thanks,
James.

[55mpg06]

Greetings.

There has been a post covering MKII (85-92 VW IDI) tach problems that you might want to check out. The same ideas should applies to the 1.9 MK3 TD. Here is a link to the post.

It could be either a loose or broken tach signal wire coming from tach or the regulator in the new alternator could possibly be faulty. Check the connector going to the alternator and see if wiggling it (careful of hands) will make a difference. In my experiance, often times it is not the guage itself that is the problem.

Hope this helps.