FWIW I followed a similar thing on the Bonneville. They didn't have a metric/eng switch starting in 97, yet it was kinda listed on the diagrams. I hunted it down to find that GM added the wire from the ground to the dash main connector on all cars. The wire was not in the dash for the US models, Canadian had the wire from that connector to HUD. Was pretty interesting to see the ways that save production costs etc.