the white wire goes to a ground terminal on the switch, which actually gets it's ground from the rotary knob, one way dims the dash lights, full the other way puts a ground to the dome lite - the other wire is supposed to be orange, maybe with a white runner, and it goes to the switch terminal labeled "D" as in dome, which should be hot anytime
if you disconnected the ground wire from the switch and the light stays on, then you've got a short along the line somewhere, an ohm meter from the switch end of the wire to the light socket should confirm that - prolly a wear spot up the windshield pillar which is pretty raw inside, but it may be at the light
Bill
