Oil pressure sending unit on manifold 305

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duece1951

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I have a1984 GMc C15 with a 305 all the smog equipment is cut out. My oil pressure sending unit on the manifold has one brown wire that is cut, or missing the connection. I see no brown wires at all that don’t go someplace other than one that comes out on the left of the engine with 5-6 other wires into a connector, which is not hooked to anything. Gauge is maxed at 60psi all the time. I know it’s not hooked up but I don’t know where to find the wire coming out of the firewall. Any help would be great!
 

GTX63

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That is the OE wire and factory boot on one of my k10s. The wire comes thru the bulkhead connector and into a loom. The video below might help.
If you cannot locate the wire or it is gone, you can run a power wire from the oil pressure gauge terminal (sending unit side) directly thru the firewall and to the sending unit.
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Ricko1966

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I have a1984 GMc C15 with a 305 all the smog equipment is cut out. My oil pressure sending unit on the manifold has one brown wire that is cut, or missing the connection. I see no brown wires at all that don’t go someplace other than one that comes out on the left of the engine with 5-6 other wires into a connector, which is not hooked to anything. Gauge is maxed at 60psi all the time. I know it’s not hooked up but I don’t know where to find the wire coming out of the firewall. Any help would be great!
Do a search, "Bulkhead wiring" 2nd from top should be a pic of a 77, with wires labeled for an ls swap. Now you don't have a sender in the manifold you could have a sender or switch at one of 2 places one is on drivers side of block above the oil filter other possible location is by the distributor in the block just behind the intake manifold. If you have a truck with a gauge you need a sender for your year truck if someone used a switch your gauge will always peg when running.
 
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duece1951

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I have both by the oil filter, two wires hooked up. The other is on the mani and is not hooked up.
 

Ricko1966

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I have both by the oil filter, two wires hooked up. The other is on the mani and is not hooked up.
Again SBC does not have an oil pressure sender or switch in the manifold. If you have a switch or sender by the distributor and you have a gauge you need to verify that you have a sender not a switch and the search I told you to make will show you where the oil pressure switch/sender wire is at the firewall. If your truck has a sender and a 2 wire switch the 2 wire switch is for power to the electric choke when engine is running.
 

Rickf

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Is there any reason why swapping the working gauge with the "non working" gauge to check if the problem moves with the gauge or stays with the truck? Kinda a run on sentance.
 

Ricko1966

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Okay starting to make more sense. Do you have a sender and a switch by the oil filter,or a single 2 wire switch by the oil filter. And 1 more time no Small Block Chevy ever!!! Had an oil pressure switch in the intake manifold. If you are talking about a switch or sender screwed into the block by the distributor we are on the same page. If you're looking at something on the manifold it's not oil pressure.
 
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RustyPile

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I have both by the oil filter, two wires hooked up. The other is on the mani and is not hooked up.
Like Rick said, the oil pressure is NOT monitored at the intake manifold. 99% of SBCs monitor the oil pressure via a sender screwed into an oil passage at the top of the block immediately behind the manifold and slightly under the distributor.. You should have 2 sensing units -- one at the top of the block as previously described. This one will monitor the oil pressure. It will have 1 wire attached to it.. A gauge requires a different sending unit from an oil pressure light.. The sender down by the oil filter is used to control voltage to the electric choke.. It should have 2 wires attached to it. Post pictures of both sender locations and we can better see what you have.

A factory wiring diagram will illustrate wire colors, components, switches, relays, and the position of wires in connectors including the firewall (bulkhead) connector. This diagram is a necessity when doing any electrical work. A service manual will explain (in a technical language) how to conduct certain tests.
 

RustyPile

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Is there any reason why swapping the working gauge with the "non working" gauge to check if the problem moves with the gauge or stays with the truck? Kinda a run on sentance.
At this point, it isn't a good idea to conduct a parts substitution.. If the fault is in the wiring and has cause the gauge to fail, the same fate would occur to the good gauge. Let's get to the root cause of the inoperable gauge first. Plus, it's much easier to check and test circuits with the instrument cluster still in place.
 

Ricko1966

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At this point, it isn't a good idea to conduct a parts substitution.. If the fault is in the wiring and has cause the gauge to fail, the same fate would occur to the good gauge. Let's get to the root cause of the inoperable gauge first. Plus, it's much easier to check and test circuits with the instrument cluster still in place.

My gut tells me he has 2 senders and one switch,or 2 switches and 1 sender and the wires hooked up wrong. O.P. if you have 3 oil pressure switches/senders we are getting close to the problem.
 
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RustyPile

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My gut tells me he has 2 senders and one switch,or 2 switches and 1 sender and the wires hooked up wrong. O.P. if you have 3 oil pressure switches/senders water getting close to the problem.
That's my thoughts also.. Trying to read oil pressure from a gauge hooked to a switch.. Pictures will tell the story...
 

duece1951

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It was getting dark out or I would have taken pics. Thank you for all the info! I will get pics and post tonight. Again, I really appreciate all the fed back!
 

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