The needle on the tachometer isn't moving at all. Also experienced some problem with the speedometer, which after passing about 80km/h displays to high of a speed. Seems like it's slow in displaying a decrease in speed and kind of add up acceleration after passing 70-80km/h. Might these problems be correlated ?

What to do next? Tips on troubleshooting, what the major problems usually are when encountering a malfunctioning tachometer.

Best Regards,
Marc