Oil Pressure Safety Switch Help

I am confused on this a bit. Trying to add a safety switch but it appears not all 3 prong ones are alike. Even these diagrams have different callouts to each prongs. I just received a Ps-127 and there is not continutity between any of the prongs. I thought at least one pair should connect to allow power through to the pump at start up. Maybe this one if faulty?

I have a Ps-64 coming as well.

Thanks.

 

Not to mention there are no marks on this switch I received today.

 

First, each of these oil pressure switches is application specific. There's no guarantee (it is unlikely!) they will perform like the Holley switch. For example, the ones Jeep uses in the 80s cars control the thermoelectric choke. They are ON when there is oil pressure, ie when the engine is running. This prevents the choke from unloading until the engine is actually running and warming up. Some of these Jeep parts have two terminals and some have three, with the third unconnected. Other non-Jeep parts are used for an oil pressure indicator light; these will be backwards from what you want, ie open (off) when the engine is running.

With the switches you have, I suggest you actually plumb it to the engine and test what it does with and without oil pressure. That's the only sure way to map the operation IMO. Pretty easy with some wire, push terminals, and your multimeter.

Unless you have some kind of timer or dash override switch added, this circuit has the following states:

Key off, engine off, oil pressure switch (OPS) open, fuel pump off.
Key on, engine off, OPS open, fuel pump off.
Key to start, engine cranking, OPS open, fuel pump on.
Key on, engine running, OPS closed, fuel pump on.

That's it. The fuel pump will run when you are cranking or if you have oil pressure. You can do this with a single on-off OPS, no need for the three terminals. Both the OPS and the start terminal on the ignition switch connect to the relay that runs the fuel pump. You should put a diode in the wire that connects to the start terminal of the ignition switch. This will prevent the signal (voltage) from the oil pressure switch from running the starter after the engine starts. If you have an OPS with a NC (normally closed) connection, you can use that to the starter switch terminal in place of the diode.

 

Go to NAPA and ask for a carter generic oil pressure safety switch. I'll look later and see if I can find the part number.

 

Thanks for the detailed info. Yeah i was thinking isnt all that is really needed is something that will interrupt the ignition with lack of oil pressure, and that the starter can bypass the switch and go right to the pump as well. So whenever the starter is on, the pump will be.

I am hoping the PS64 that is coming today will help.

 

That would be great. I did look on line and is one but it doesn't look like a Carter as its a NAPA brand. I have to order though.

 

This appears to be a typical GM fuel pump electrical circuit.
The pressure switch electrically is: Terminals "I-P" normally open. Terminals "S-P" normally closed. System operates as follows.

Engine Off: Ign. switch on (run position), power from Ign switch to terminal "I" on pressure switch. Nothing happens. Ign. switch to start position, power sent to terminal "S" on pressure switch to terminal "P" to pump relay activating the fuel pump.
Engine on (running): Pressure switch closes terminals "I-P" and opens terminals "S-P". Fuel pump relay now receives power from activated pressure switch maintaining fuel pump operation until ignition switch is turned off.

 

Got it done and working. In case anyone in the future wants this information:

The PS64 is the right switch to use or order from your favorite FLAPS.

Also i added a relay.

Thanks for the help.

 

well it appears after sitting a little bit while i rebuilt the rear brakes, seals, bearings, etc. that the new oil pressure switch is already failing. Checked the wiring, and the relay and appears ok. Will get and throw in a new one and see. So frustrating...

Anyone else have experience with these failing easily or often?