lone microswitch on valve cover, what is it?

[harpua00]

1985 300d. The lone electric microswitch on the valve cover. Looks like it gets triggered only at full throttle. What does this do? Mine actually seems to be out of adjustment so even at full throttle you need to push it in just a bit further with your finger before you can hear the click. What is the purpose of this switch? I found lot's of info on earlier model year "3/2" valves with vacuum lines running on the valve cover, but this is distinctly different, only two small electrical wires going to this one.