Diagnostics only work on the engine and ABS at that age.
This is the circuit for the glovebox light
http://s2-audi.co.uk/workshop/schema...ul92/page3.png.
Grey / green wire goes more or less direct to fuse 14.
Does your car have autocheck ? If it does, it will also go to T26 pin 1 for the dash cluster. T26 is yellow.
From there it goes to E20 which is the dash dimmer