It'll more than likely just be the bulb that has gone mate. Theres a single tiny capless bulb fitted behind the controls that simply pulls out. These often go on mk3's seeing as they're bloody old now. Just pop the facia off from around the three heater dials and remove the ashtray then you'll see 4 screws holding it the centre section of the dash in. Withdraw the controls and on the back of them you'll see a white plastic shroud, pop that off and you'll see the bulb and green filter surround. VW sell them for less than a quid.
