It sounds like he found the dimmer wire for the car but connected it to the wrong wire on the empeg to me.

Right. I agree that the car's actual dimmer wire is connected to the wrong wire on the empeg. That would be completely consistent with the symptoms.

My point is that since the empeg wires are quite clearly labeled, and car wiring harnesses are never labeled at all, then it's more likely that the mistake was made due to lack of car-harness knowledge rather than lack of empeg-harness knowledge.