oil pressure switch tee problem

[Jonathan Sherman <jsherman@mail1.i1.net>]

Why is it that when I added in a Tee for the oil pressure switch...  the 
light goes on when oil pressure is good and the light goes off when the 
oil pressure is too low?  FYI, the oil pressure switch is of the 3-wire 
variety and I put a mechanical oil pressure gauge on the other part of 
the tee.  

-jon