Two prong oil pressure sensor

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Baker7888

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Dec 3, 2021
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I have the stem behind my intake manifold which goes to a 2 prong oil pressure sensor and ties to my wiring harness. I will be running a Holley red fuel pump which recommends wiring in an oil pressure sensor as a safety. Am I able to tie into this one and if so, how?
 

pagrunt

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I have the stem behind my intake manifold which goes to a 2 prong oil pressure sensor and ties to my wiring harness. I will be running a Holley red fuel pump which recommends wiring in an oil pressure sensor as a safety. Am I able to tie into this one and if so, how?
It does kinda work like safety switch from how I've looked at it over the years. One blade obviously trips the light at low pressure, the other blade powers the choke with a fused lead in the fuse box. Since it closes when pressure hits that oh-no level for the light it should do the same for the fuel pumps safety stop by, my uneducated guess, grounding out that circuit. Might even be able to repurpose that choke circuit by running a lead from the choke's plug to the pump/relay & use it's fuse.
 
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Baker7888

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Dec 3, 2021
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It does kinda work like safety switch from how I've looked at it over the years. One blade obviously trips the light at low pressure, the other blade powers the choke with a fused lead in the fuse box. Since it closes when pressure hits that oh-no level for the light it should do the same for the fuel pumps safety stop by, my uneducated guess, grounding out that circuit. Might even be able to repurpose that choke circuit by running a lead from the choke's plug to the pump/relay & use it's fuse.
I am going to plug the safety switch into my factory harness connection. So this trips the dash light, I am a little confused on the choke part you mentioned. Wondering if I can just splice into factory connection where the fuel pump install directions call for oil pressure safety switch
 

pagrunt

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Sep 14, 2014
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I am going to plug the safety switch into my factory harness connection. So this trips the dash light, I am a little confused on the choke part you mentioned. Wondering if I can just splice into factory connection where the fuel pump install directions call for oil pressure safety switch
My theory is that the the brown wire to that plug would be used as the fused power, the light blue from it to the carb choke would be the feed to the pump/relay. Then when the oil pressure get to the trip pressure it'll close the switch which as it turns on the choke/oil light, with my theory it'll ground the circuit & shut off the pump/relay cutting off the fuel supply. If this all works as I'm presenting it here, just splice it at the choke plug. Again, just my theory on how it could work.
 
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Baker7888

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Dec 3, 2021
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My theory is that the the brown wire to that plug would be used as the fused power, the light blue from it to the carb choke would be the feed to the pump/relay. Then when the oil pressure get to the trip pressure it'll close the switch which as it turns on the choke/oil light, with my theory it'll ground the circuit & shut off the pump/relay cutting off the fuel supply. If this all works as I'm presenting it here, just splice it at the choke plug. Again, just my theory on how it could work.
Well I appreciate the thought and I like the idea. Ill see if others chime in, maybe somebody who is running an elec. fuel pump. The instructions suggest I use this (see pic) oil pressure safety but my thinking is I already have one, why need two.
 

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78Delta88

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I have the stem behind my intake manifold which goes to a 2 prong oil pressure sensor and ties to my wiring harness. I will be running a Holley red fuel pump which recommends wiring in an oil pressure sensor as a safety. Am I able to tie into this one and if so, how?
Did yours start out a q-jet or TBI from factory?
 
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64nailhead

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That switch was utilized by GM on H-bodies as well that employed an electric fuel pump for a 4 cylinder carved motor.

I owned one as a kid, when the car quit it needed oil haha.

It really didn’t work as well as they intended imo. The carb had to run out of gas which didn’t occur very quickly.
 
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Baker7888

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Did yours start out a q-jet or TBI from factory?
It was the 3.3 L 200 CID v6. It had a carb, i believe it was a quadrajet. I have an LT1 in it now but using the sensor off the 3.3

The $44 sensor from Holley has this description on Summit:

"Holley Safety Fuel Pressure Switches

It's always a good idea to place a safety switch in the circuit when installing an electric fuel pump. Holley safety fuel pressure switches will ensure the electric pump will not work unless the engine has oil pressure. It will prevent the pump from running in a situation where the motor may stall with the ignition on. Wiring the switch through the starter solenoid circuit energizes the pump on engine start-up. After the engine is running, the switch continues to provide power to the pump as long as there is oil pressure to keep the switch turned on."

I dont have an issue running the Holley unit, I just dont want two oil pressure switches off the back of the motor. The Holley unit is 3 prong. Can I incorporate the Holley one into the factory wiring instead (to my understanding, activating low oil pressure light and electric choke??) and abandon the factory two prong switch?
 
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78Delta88

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Yes you can. Do you have pic of the piece we are talking about? I'm not familiar with the LT1 specifically, yet on the TBI, GM used 2 different units. A 3 connector and a 2 connector. ECM runs the pump for about 8 seconds and car starts. Everything through that switch keeps the pump running as long as you have oil pressure. When it goes bad you get a no start that is difficult to diagnose for the pre-OBDII crowd.

What is the year and model of your car?

What is the year of the LT1 you are using?
 
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Baker7888

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Yes you can. Do you have pic of the piece we are talking about? I'm not familiar with the LT1 specifically, yet on the TBI, GM used 2 different units. A 3 connector and a 2 connector. ECM runs the pump for about 8 seconds and car starts. Everything through that switch keeps the pump running as long as you have oil pressure. When it goes bad you get a no start that is difficult to diagnose for the pre-OBDII crowd.

What is the year and model of your car?

What is the year of the LT1 you are using?
Ok it is an LT1 but running a carb and HEI so no ECU whatsoever.

Right now i have a two prong sensor from 78 malibu 200 CI V6 (original motor/wiring harness)

Also attached is a pic of the Holley suggested unit
 

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