2GM20 Oil Pressure Switch
- Thread starter Clark
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I'd dissagree
The oil switch is normal open and low oil pressure closes it. That completes the circuit to ground and lights the idiot light and buzzer.
To test, take the lead (should only be one) off the unit and ground it. The buzzer should sound. When you unground the lead the buzzer should go off. Then test the sender for continuity upon low engine oil pressure and an open when the pressure is high.
The oil switch is normal open and low oil pressure closes it. That completes the circuit to ground and lights the idiot light and buzzer.
To test, take the lead (should only be one) off the unit and ground it. The buzzer should sound. When you unground the lead the buzzer should go off. Then test the sender for continuity upon low engine oil pressure and an open when the pressure is high.
Yup, that's how mine works.
I once had the wire chafe through where it met the engine block. The dang buzzer would sound intermittently. Drove me nuts till I found it. I knew it wasn't 12v to the sender and assumed it was a normally open circuit until the ground circuit was closed.
I do agree with Alan though, no way should that buzzer continue once the key is off. The circuit must be getting power from somewhere else.
I once had the wire chafe through where it met the engine block. The dang buzzer would sound intermittently. Drove me nuts till I found it. I knew it wasn't 12v to the sender and assumed it was a normally open circuit until the ground circuit was closed.
I do agree with Alan though, no way should that buzzer continue once the key is off. The circuit must be getting power from somewhere else.
Switch is closed or shorted to ground when there is no pressure (center post to pipe threads).. It should OPEN when it sees pressure around 2 PSIg. Makes it kinda failsafe.. a short to ground in that circuit will give an alarm even when pressure is OK..
Great Info guys. It makes sense that it is normal closed
so that when the switch is on and engine not running, the alarm sounds (closed circuit) to indicate no pressure and when oil pressure rises, it opens the circuit and alarm goes silent.
We'll look for a wiring problem.
so that when the switch is on and engine not running, the alarm sounds (closed circuit) to indicate no pressure and when oil pressure rises, it opens the circuit and alarm goes silent.
We'll look for a wiring problem.
common naming problem
Do I name the switch for its "normal" position when the engine is on or off.
It spends most of its time off and that is what Id see if I was working on it but "normal" is when the engine is on and up to temp and batteries are charged..... steady state running is normal. For house wiring it is what position it is in based on time.
So Clark, you got the schema of things right bu,t like most, you named it for what you are looking at not what you would buy in the store. The oil pressure switch is "normally" open
Do I name the switch for its "normal" position when the engine is on or off.
It spends most of its time off and that is what Id see if I was working on it but "normal" is when the engine is on and up to temp and batteries are charged..... steady state running is normal. For house wiring it is what position it is in based on time.
So Clark, you got the schema of things right bu,t like most, you named it for what you are looking at not what you would buy in the store. The oil pressure switch is "normally" open
Just a semantics note.. A switch is normally named in its stand alone state.. no input.. so a switch like this oil pressure alarm switch would be "Normally Closed" since with no oil pressure input, it is closed.. the naming is not in its state of use.. but rather in its no input state.. This is a convention of naming instruments and sensors ..
Bill, we both agree on the operation of the circuit but we appear to disagree on the semantics. A normally closed device, in this case a switch, means the circuit is 'complete' or 'closed' when not exposed to any outside influences. Only after exposure to the outside influence of oil pressure does it open.
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