Im hardly knowledgeable but had similar problem with my 94 westy 1.9. Soon thereafter dash lights failed. Then more unexplainable annomalies followed. I put my woes to the grp. One said i should replace my light switch. I didn't listen. Lived with it for a year using cel phone screen light at night n freaking every time tach bounced... Dumped a bunch of money into series of other things. Finally began to think i was going blind cause my lights seemed dimmer. Then i got pulled over 'cause of break light outage. Bulb replacement didn't work. Finally an old guy at omalleys said check ur light switch. I replaced it. A $20 , 10 minute diy fix. All my problems went away. 
U learn how stupid u r  when u own a westy. Start with the simple no matter how much u want to make more of the problem. In the words of the late great w.c. fields, "theres a sucker born every minute."
For what it's worth,Eve

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  On Wed, May 18, 2016 at 10:37 PM, Mike Miller<mwmiller6@ATT.NET> wrote:   Volks, and oil head Volks,
Got a TDI conversion with a diesel cluster [Thanks again Roger!] 
The tach occasionally starts bouncing around from 0 to 4-5000 rpm. Tried lubing it but the problem reoccurs.
Is there anyway the pick up [where ever it is and however it works] could have an intermittent problem? 
Any other ideas of stuff to try?
TIA
Mike from Cotati