Well I don't know if mine is different because it's a euro, but if you pull the headlight knob straight out towards you (like you're turning on the front fog lights) there should be (again, at least on mine) a bright red light coming from one of your tail lights, the driver's side if I remember correctly. You can't miss it!!! It's bright! So if your front fogs are on, and there is nothing coming from your tail light, then either you don't have that or it's not working.

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'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."