Originally posted by azdave
So here is where you are. Temporarily grounding the black/yellow wire simulates the dimmer knob being turned all the way up. If you are busy you could leave it this way for now with no harm until repaired later but your dash lights would always be at full brightness. The performance of your headlights have nothing to do with this problem. This problem we are chasing is only affecting the dimmable lights inside the car and nothing else. Yes, the dimmer knob will do nothing right now. The function of the dimmer knob is effectively bypassed as long as the black/yellow wire remains temporarily grounded. If you want the dimmer knob to function properly you will need to check the wires feeding it. Note: The factory service manual contains an error when it comes to the dimmer unit wire schematic. The manual shows that the knob has a dimmable light bulb inside to illuminate it at night. It does not. If you can unplug the connector on the back of the dimmer you could perform a similar test as above. To do this test you will first have to disconnect the two wires you spliced in the first test or you won't get valid results. Again, you will want the marker light switch turned on for this test but not the ignition or headlights. One wire to the dimmer unit will be a constant ground wire. The other wire will be the same as the black/yellow wire we have been testing. If you have the connector unplugged and dangling down, take a paper clip and touch the two terminals inside the connector shell together. This should produce the excact same results as the first test. If you don't get full bright dash lights with this test then you know you have a cut wire feeding the dimmer. If you DO get full bright dash lights with this test then the dimmer unit might have failed (but try to plug it back in a see if maybe it was only a loose connector).