Technical Oil pressure safety switch wiring help

If Hath follows my post #17 & #26, he will be fine. The relay & circuit is ok...

"With ignition wire (86)(yellow) disconnected from C on the oil switch, there is no power to the purple (87) or yellow (86) wires at the relay. Not even when cranking. Nor is the fuel pump kicking on.

When I attach 86 to C the pump turns on, and 87 and 86 get power at the relay."

The relay has 4 leads. Red full time 12v+, Gray ground, purple output to pump, yellow relay control wire. Hath verified relay and pump are ok by his post quoted above.
Now it's finding out why the yellow relay control wire is engaging the relay when it should only be getting power when 1) cranking 2) ignition key on & oil pressure is over 5 p.s.i.



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Ok here are the results of more tests, let me know what you think:

Continuity tests (no wires hooked to o/p switch:
C to NO = 1
NO to NC = 1
C to NC = 000
Switch housing to ground = 000

So faulty switch?

On to the wiring:

When only C is connected: Pump does not turn on, even when cranking.

When C and NC are connected: Fuel pump turns on with key off.

When C and NO are connected: Pump does not turn on, even when cranking.

Ignition wire gets power when key is on, or when cranking.

The wire that goes to NC is from the battery, so it has constant power, not just when cranking.

NC on the O/P switch does not get power when cranking (while C and NO are connected).

What say ye?

 

Let me digest all this!
When you give resistance checks...you mean

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I hit reply too quickly. I'll start over.
Resistance checks...you mean 1=1ohm, correct? 000=zero ohms (dead short) 1 ohm is extremely low, almost zero.
If that's so, then your oil pressure switch is bad. Nothing hooked to it, no oil pressure then a good switch C to NC ,zero...C to NO infinity (open).

Next problem..."When C and NC are connected: Fuel pump turns on with key off."...since NC goes to starter solenoid, there should only be power on NC during cranking. Starter solenoid should not have power with key off...apparently that wire is connected improperly. NC wire has to go to starter solenoid, not battery terminal.

"Ignition wire gets power when key is on, or when cranking."
This is wrong. The oil pressure switch NO terminal goes to ignition switch on terminal, typically the ignition coil + terminal. It should only have power with key on.

Copy/paste from what I said before...

"Disconnect yellow relay lead to C.
With voltmeter or test light verify 12v+ power oil pressure switch NC only when cranking. 12+ @ NO terminal with key on ONLY (off on accessory & key off)
12+ @ C when cranking and motor running."

So oil pressure switch, power to NC cranking ONLY. Power to NO ignition switch on position ONLY. This way C has power only if motor is cranking, car is running with oil pressure. C will have zero volts when oil pressure is below 5 psi OR key is off.

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I need to add one detail...you don't have anything like an Accusump...anything to hold oil pressure? That could foul up resistance tests if when motor is off you still have any pressure above 5 psi that would keep the oil pressure switch on.

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When I switch my multimeter to the continuity setting, 1 means there is no continuity, 000 means there is great continuity.

 

Then that changes everything with your resistance checks. So...
"Continuity tests (no wires hooked to o/p switch:
C to NO = 1(infinity)
NO to NC = 1(infinity)
C to NC = 000
Switch housing to ground = 000"

Your resistance checks of the oil pressure switch means it's okay.

Your problem is the wiring going to the switch.
1) C terminal should have one wire...the yellow going to relay.
2) NC terminal should have one wire...going to starter solenoid. Jegs says solenoid S terminal. With test light/voltmeter on starter solenoid have a helper crank it...just for a second. You want power only when cranking. Connect this NC wire to that.
3) NO terminal should have one wire...going to ignition "on" position only. If you have an ignition coil it's the + side. With test light/voltmeter be sure power is there with key on only...not off, accessory or cranking. Connect this NO wire to there.

You're done.

Key off...pump off. Key on...pump should be off because you don't have oil pressure YET. Key cranking...pump on. Motor starts, key is in on position, pump on. Turn motor off...pump off. Key to accessory...pump off. This makes the final check. All wires away from heat source, neatly zip tied, etc.

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3) NO terminal should have one wire...going to ignition "on" position only. If you have an ignition coil it's the + side. With test light/voltmeter be sure power is there with key on only...not off, accessory or cranking. Connect this NO wire to there.

Note!!!!!
I found a snafu...eliminate above paragraph, substitute this one...

3) NO terminal should have one wire...going to ignition "on" position only. If you have an ignition coil it's the + side. With test light/voltmeter be sure power is there with key on only...not off or accessory. Connect this NO wire to there.

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Is this a race only car?
There is no way I would run such a switch on a street car.
For simple safety reasons, you might need to run an engine with 0 oil pressure..... like to get you out of harms way.

 

Wow, I'm thinking that this is the first time I have seen such a simple problem get so beat to death. ..

 

With the key off, there should not be 12 volt power to any terminal on the oil pressure switch. You say when you connect the Common terminal on the pressure switch, the pump runs without the key on. Check the NO and N terminals to see which has power. I suspect the wire from the starter is not on the S terminal but a different terminal that is powered. If the S terminal was powered, the starter would be turning. If you don't want the fuel pump to run while cranking, remove the wire from the N terminal on the pressure switch. The oil pressure will build up while cranking and the pump will turn on if the engine cranks very long before starting.

 

Hath is close to a solution. He's down to two connections is all, NC & NO.
Let's see how it works out.
We never had this setup even on our drag cars...but that's irrelevant at this point.
We just had the master cut off switch required at the back.
I'd never ever want to have any motor with a pressurized oiling system with zero oil pressure though regardless of what load or r.p.m.!

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https://perkypetes.club/gm-starter-...-site-info-illustration-solenoid-connections/

 

Please...

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So I think you guys helped me out. I didn't realize I had to go the the s terminal on the starter solenoid, in my defense this one isn't a post terminal, rather a connector. So splice into the wire that goes to "s"...at least I assume that is s?

 

From what I can see that's it. Easy to tell with light or meter. It will have power ONLY while cranking.
That "only while cranking " power...wire to NC. NO to ignition on ONLY power (coil +).

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Fixed! I had ran one wire wrong. Go to the s terminal on the solenoid, not the constant. Special thanks to sevenhills1952!