Resistance Test
WARNING: This page is about a different car, the 2001 Audi allroad, 2001 Audi S4, 2001 Audi A6, and 2001 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect negative battery cable. Disconnect terminal D+ (Blue wire) from generator. Connect ohmmeter leads between positive battery terminal and Blue wire. Turn ignition on. Resistance should be 140-160 ohms. If resistance is not 140-160 ohms, check generator bulb. If bulb is okay, check Blue wire for open or short. If blue wire is okay, replace instrument cluster printed circuit and retest.