My bulb on the headlight switch was burned out too...

And you pull out two clicks to activate the rear fog. A single click activates the fronts only.

If you pull two clicks, the orange light on the switch should glow, and the rear fog bulb illiminates.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car