[tech] oil pressure switches

["Wm. Josiah Erikson" <josiah@gsinet.net>]

OK, my Bentley is pissing me off. It's contradicting itself again. But
it's an old one, made in 1983. Maybe the new one doesn't have so many
mistakes in it... Brian?
Anyway, I'm dealing with an '84 Scirocco that has the following
condition: The oil pressure warning light and buzzer stay on for much of
the time. When the light goes on or off doesn't seem to have much to do
with anything at all. So I figure I'd see if the oil pressure is good,
and since I don't have an oil pressure guage, I figured I'd check
whether the oil pressure switches were setting off the buzzer or whether
it was something else, and if it was the switches, I'd replace the
offending one with a used one I had around, and then if the condition
still existed, conclude that the oil pressure was bad, or at least take
it somewhere to have it tested.
So I looked in the trusty Bentley, and it tells me two contradictory
things:
1. That the switch on the cylinder head is normally closed and that the
switch on the oil filter bracket is normally open.
2. If I disconnect the wire that goes to the switch on the oil filter
bracket, the warning light should come on and a buzzer sound.

Obviously, these two things are contradictory. If the switch on the oil
filter bracket is normally open, then disconnecting the wire should make
the light go out, if anything. So... what's right?

And somebody could tell me what the switch ratings mean, like "a
normally closed 2.1-6.4 psi switch". Does that mean that it's closed
between those pressures? Seems odd, because I thought that our engines
ran up at like 60psi oil pressure.

Anyway, if somebody could enlighten me as to how these switches work,
I'd be eternally grateful : )

    TIA!
    -Josiah


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