[MBZ] Unknown wire

[Dennis Perkins]

I was cleaning under the hood of my 84 300SD today and found a three lead 
wire that ends in an oval female connection behind the drivers side 
headlight next to the preglow timing relay.  It starts at a contact (looks 
like a magnetic pickup) next to the timing mark.  I can see no connection 
that it should hook to.  Everything in the car works.  Does anyone have any 
idea as to wether this is some kind of diagnostic connection or should it 
hook up to something.