The only one I've ever seen light up was on a '75 450SL the other night..which prompted this whole thing to begin with..? Do you supp. the PO tried to put a bulb in there too at one time??..to no avail???...It looked like a nasty 20 yr old bulb that I pulled out...or, maybe they all come with that bulb in place, yet not wired for the rear fogs????

Will always be a mystery to me, I guess...

sean