Erratic guage readings!

[MJK 24]

I've got a weird problem with the coolant temperature and fuel guage on my Mk2 Scirocco. It has happened a couple of times in the past 12 months but now it has happened three times this week.

There's two different scenarios:

1) Both guages will over read by 5-10%. If I turn on the dipped beam headlamps, the guages will read correctly but the clock goes off, and the main beam tell tale LED illuminates and the main beam will be on regardless of the position of the column switch to operate them

2) Both guages will under read by 5-10%. If I turn on the dipped beam headlamps, the guages will read correctly.

The only thing I can point out is that on the Mk2 Scirocco, the headlamps do not operate via a relay. They're switched directly from the switch.

Any ideas on where to look?

Thanks :)

[mark1gls]

Check the earth wire on the back of the rocker cover in the engine, there should be a brown wire on a ring connector connected to one of the rocker cover studs, check it's not hanging on by a couple of threads of wire, it's the earth for the instruments. If that ones OK check the earth wire running from the back of the instruments but you may need to remove the instruments to get to it but it may be possible from underneath the dash.

[DT1]

Check the earth wire on the back of the rocker cover in the engine, there should be a brown wire on a ring connector connected to one of the rocker cover studs, check it's not hanging on by a couple of threads of wire, it's the earth for the instruments.

Whilst you are there, check the braid that goes to the coil holder on the bulkhead. It should be on the same bolt that the ring connector is attached.