When you say switch, do you mean the toggle switch that comes with the foglight kit or the new headlight switch? I only ask because I did the conversion on my 04. 5, and all I needed to do is install the underbumper harness, the lights, and a new foglight/headlight switch in the dash (not included in the kit). Worked like a charm. I didn't need the entire loom or the toggle switch, etc. No reflash either.