Buzzer of Doom wiring incorrect? Odd.

[logicred]

1987 1.9 DG engine. Previous owner had unplugged the ribbon cable to the back of speedo for the oil pressure warning light. I reconnected it and got buzzer of doom after 2k revs. Points to the 'normally open?' low pressure switch near the pump, or wiring from the switch, or possibly circuit board from what I have read (or maybe even low oil pressure lol!).

I wish to test the buzzer circuit first (and isolate the switch) so have naturally taken off the wire to the oil pressure switch near the pump and grounded it to earth which should simulate the switch being earthed (closed) and thus indicating all good oil pressure, but it still sounds the buzzer after 2k revs. When I take the wire away from the earth, in theory this should make the buzzer go on, but it actually turns it off!

So bottom line is, it looks like the wiring is acting differently to what it should, or am I missing something! It's as though I should be using a GREEN oil pressure switch (normally closed).

How do I test the oil pressure switch by the way?

Thanks in advance.

[937carrera]

1.9DG could have a grey or a white DOPS "High" pressure switch. Could also have a black one, if PO has uprated / downrated from original https://www.brickwerks.co.uk/brickwerks ... -switches/

As you say, normally open, so when you earth the cable it should silence the buzzer

Your test seems correct so I think you are going to have to trace the wires from the dash through to the engine bay. It almost seems as though the "Low" pressure cable to the switch is connected to the "High" pressure wiring in the loom / junction box.

I assume you have a wiring diagram, if not http://syncrosport.com/info/wiring/