on a lot of vw watercooled engines there are two oil  pressure
switches.  one up on the head and one at the  filter/oil pump head.
they are of two different values and types.  the one on top is a normal
closed type (and is the same used ever since bugs) and the one below is
a normal open type.  the specs for the bottom one are that it should
trip if pressure is reached and engine rpm is above a certain point.
dont remember the exact speed but it is above idle.  the circuit in my
jetta (inside computer or chip behind dash) that was supposed to
differentiate between a real alarm and not a false one failed.  (had
fun trouble shooting that.)  too expensive so i just went to a double
idiot light.  green for pump pressure is good  and red for top end isnt
getting any oil.  the bottom one can be replace with a lower pressure
one but finding it in the normal closed ones is a little harder to do.
jimt