Tach not working?

Replace your ovp relay.

Maybe it will fix the odo too.

I think you have a different rear end or a different cluster causing the speed difference

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87' 300DT (Grey w/ red leather)
87' 300TDT (silver w/ palamino tex) SOLD

2012 VW JSW TDI (on tdiclub.com all the time "btcost")