what's this switch for?

[rfpmoxie]

what's this switch for?
'90 300SL Hello all. As I try to figure out why my 16 month old battery went to 1.5v but has been holding a full charge for 3 days(72 hrs) now, I've replayed what I did since shutting it down on Saturday noon and the dead batery condition of Monday morning 7AM (43 hours). I've eliminated cleaning the inside, but I re-looked under the hood to see what I may have done while "dusting", checking the fluids, etc. Still coming up without an answer, I've noticed a switch (I think) with a tall ~3/8" black plastic actuator(stalk) coming out of the top of it and must be engaged and/or disengaged when the hood is up. It is located just before the covered section at the firewall on the passenger side where the diagnostic connector, w/w relays and other electronic goodies are located. Likely, this has nothing to do with my problem, but it would be good to know what it is.
Thanks for the help, Ron