At 02:30 PM 8/1/2010 Sunday, David Clarkson wrote:
>If no fault is found with the wire I'll try Marvel Mystery Oil. It's great

The switch should close (i.e. short to ground) when the pressure gets
up to about 13 psi.  Below that it should be open.  I'd be very
surprised if there were something blocking it so effectively that the
pressure couldn't get through.  Inside the switch the oil presses
against a diaphragm, so there's nothing to stick there.  Water could
get into the outer part of the switch and corrode things, or the
diaphragm could leak and fill the whole switch with oil.

Yours,
DAvid