My friend has one for sale, but he goes to Texas for the winter and the sign is in Michigan. If you don't find one by May, give me a holler and I'll see what I can do for you if your still interested in one. I think he wanted around $500. Here is a dusty picture of it.
I tried to get to mine but my non-gutted 850 is three pumps deep, and I can't get the skins off while its buried (and my access door is 'painted' shut). Sorry. Maybe someone else can get to theirs. I may have to move a few pumps around next week to make room for a new purchase. I might be able to get to it then.
Looks like no one has ever seen this type of light switch on a Tokheim 850. It was placed on pumps with serial number range 369,972 - 499,999. I purchased a copy of the Repair Parts Manual; so no I know what the knob looks like.