Going back to original OP gauge

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sikes185

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Hey guys. Not going into why I did this many years ago. But did any way I replaced the stock OP sending g unit with a Stuart Warner and gauge set up. Now I want to go back to original. Pictures are of what I found as an oil pressure sending unit for my 1985 gmc c15. 305 motor. Also a plug that is factory. The plug has 2 female connections. Looks like a green wire and a brown. The sender only has one male. On the block behind intake is a brass part that is a Y. One part has a sensor on it with an original wiring plug connected. I understand rhe choke light thing and it is on now sense installing a carb with a choke. And no OP sender. My question is can I just plug the original plug to the brown wire side to that one male terminal on the sender.
I can’t just install it and check. The distributor is out so I could get to everything. I ran a TV cable to my 700r4 also. But that is beside the point.
Thanks guys
Remember this
Not only do I appreciate you today but everyday.
Glenn
Mississippi
 

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RustyPile

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If you thoroughly understand how the choke light works, you know that when the choke light is ON, no voltage is being applied to the choke itself. The light turns off when the choke is "turned on"..

Originally, your truck was equipped with 2 oil pressure sensors.. One sensor, as depicted in your 1st picture is the sensor for the gauge.. The other sensor is actually a switch.. Voltage is applied from the ignition switch to 1 of the wires on this sensor/switch. Oil pressure (when the engine is running) turns on the switch. Voltage passes through the switch and goes out the other wire to the electric choke.. On most engines of this era have this sensor on the side of the block just above the oil filter. If you have a "T" on the fitting under the distributor, the choke switch will work just fine there along side the oil pressure gauge sensor.

I offer this advice to anyone doing repairs involving ANY type of electrical work.. Obtain and refer to a factory wiring diagram for the vehicle you're working on.. These wiring diagrams are available as free downloads all over the internet including this site.
 

sikes185

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Ok I have a green wire that always went to the choke. 12 volt when key is on. Ok I’ll study more of what you said. By no means am I an electrical guy. So it takes a few to understand. I thought that that sense that Stuart Warner sender was not in line with the harness was the reason the choke light was on. Not seeing the pressure from it. Ok I’ll figure it out.
 

sikes185

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Ok just thought of something. I think I am getting the 2 confused. The one that is still in the harness off that tee, is that the actual pressure sender and the one that I am replacing is the sensor? All sensors I have seen has 2 plugs on top that the original pig tail in the picture would plug into. And that green wire going to the choke makes sense. Am I on the right track sir?
 

RustyPile

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No, you're mistaken about the terminal count on a gauge type sensor. The oil pressure sensor for the gauge is that bell shaped metal can (in your picture) with a single spade terminal on top.. The pressure switch for the choke is a two terminal device much smaller than the gauge sensor.

If the choke has voltage when the key is on but engine not running, choke wiring has been altered or modified. Do you have a sensor or some type of switch installed in the block just above the oil filter?? You're dealing with a 40 + year old vehicle. All sorts of changes, modifications, and hack jobs could have been applied in the past.

The choke heater wire is light blue (not green) and comes from the oil pressure SWITCH. The other wire on this switch is pink with white trace. Check the wire colors in that 2 terminal plug in your picture. That green wire you speak of probably goes to the temperature sensor in the driver side head between the front two sparkplugs. Again, I urge you to obtain a factory wiring diagram for your vehicle. Wiring color codes, wire gauge, relays, switches, sensors, etc. are all shown in those diagrams.
 

sikes185

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Ok. Alittle more history on my truck. I am the 3rd owner. Bone stock when I got her 28 years ago. 305 was replaced by a 350 crate motor. This picture is of what is on the back of the block. I am guessing it was placed there by the shop that put the crate motor in for me. It is a brass Y fitting. I have not touched the right side. Looking down on it. It Has what they plugged in to it. I am thinking they just moved what was by the filter to this point. There is nothing by the filter now. On the left side of fitting is where the Warner sending unit was that I took off yesterday. I’ll get the diagram and trace what I can see.
Thank you for your time.
 

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Jgonick

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Again, I urge you to obtain a factory wiring diagram for your vehicle.
Strongly agree, learning to read wire diagrams really help with electrical questions and problems.

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sikes185

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I agree. And looked for one last night. I will get one.
Again thank you so much.
 

GTX63

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Can't recall but I think in the video they mention and show color and location of the OPSU wire.
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sikes185

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Rusty, Nick, GTX
Can’t thank y’all enough. Looking and looking for that tan wire. I saw it going to the sender in the diagram for the gauge only trucks. I found it but it was like hooked to something. Couldn’t see the end it was connected to. So I got the fat boy board out so I could lay across the engine compartment so I could see where it went behind the motor. I found it. The place that put in my 700r4 got that wire between the block and the bell housing.LOL. So I got her done. See picture. I will find me a wiring diagram for my truck and it will be in my documents for my truck.
Again thank y’all for all the help.
Take care and be safe.
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RustyPile

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One last bit of "clean up" and you'll be done.. You don't want any part of a bare wire exposed.. Solder the crimped terminal and then slip a piece of heat shrink over the entire terminal. Shrink it down with a little heat and plug the terminal into the sender.. You're done..
 

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