In my headlight switch is the pilot light. I've never been able to determine in either my 85 300SD or my 83 300D what causes this light to light. Does anyone know if this light is intended to come on in these models or is this light reserved for some other function in other models? I've checked the light in both cars and they are good. In other cars I've looked at, I've never seen one come on either. What the heck is this light for and what could be causing it to not light when the fogs are switched on (if that's what it's for)?

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1983 M-B 300D, 148K, daughter's ride
1983 M-B 300TD, 120K, my ride
1985 M-B 300SD, 102K, wife's ride
1969 HD FLH, 45K, restored/hobby
1996 Chev Suburban, family taxi/tow vehicle
1990 John Deere Model 240
1942 John Deere Model LA
1985 16' 4Winns ski boat