Oil pressure gauge problem

[Hamgrease]

Gauge maxes out without engine running, and stays there when running. Every other gauge works properly. I’ve checked the prongs top left 12v top right 8v, bottom center ground, checked top left to where it plugs into the back of the cluster 8v, when it passes through the bulkhead at the firewall it goes to over 11v . I completely replaced both tan wires from the cluster plug in to bulkhead and from bulkhead to oil pressure sensor, ohms reading 0 checking the sensor itself. I even bought a new gauge and tried it doing the same thing. I’m stumped. I put brand new grounds from frame to engine, engine to body both battery cables are new I made sure they were grounded to bare metal even the headlight ground. Both fuel tank grounds are good or they wouldn’t be working when I switch tanks. Anything else I could have missed?

 

[Blue Ox]

Did you try disconnecting the wire from the sensor? 0 ohms sounds like the sensor is shorted, if I'm reading that correctly.

 

[GTX63]

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[Hamgrease]

I checked it before I installed it and the one I removed after I removed it both had 0 ohms

 

[Bextreme04]

I checked it before I installed it and the one I removed after I removed it both had 0 ohms

Is it a single prong sensor? It should never be 0 ohms from the prong to the body. The way the gauges work is a constant 12v fed along the sensor wire to the sensor from the gauge. The sensor then varies the resistance to ground to move the needle on the gauge. Short to ground(0 ohms) will drive the gauge full, disconnecting the gauge(open) will drive the gauge to zero.

The correct sending unit for a gauge should look like this:
https://www.summitracing.com/parts/...MI-vWAj5v3hgMVHAutBh03ng2TEAQYAiABEgKiNfD_BwE

The other thing you could have is an oil pressure switch, which would be used with a light or for fuel injected vehicles to provide power to the fuel pump while it is running. The switch should be open when no pressure is applied and 0 ohms when pressurized and looks like this.
https://www.amazon.com/dp/B000IYY11M/

 

[Blue Ox]

The other thing you could have is an oil pressure switch, which would be used with a light or for fuel injected vehicles to provide power to the fuel pump while it is running. The switch should be open when no pressure is applied and 0 ohms when pressurized and looks like this.
https://www.amazon.com/dp/B000IYY11M/

Wouldn't it be the other way 'round? Open when there is oil pressure, and closed with no oil pressure to illuminate the warning lamp?

 

[Rickf]

Could always "T" in a mechanical gauge to get a second opinion.

 

[Bextreme04]

Wouldn't it be the other way 'round? Open when there is oil pressure, and closed with no oil pressure to illuminate the warning lamp?

Oh, yep... that's right. So he probably has a switch instead of a sending unit. No oil pressure when it's off, so its closed and driving the gauge off the needle high. I think there are two "switch" units also. One is a two prong unit and it is the other way around to drive the fuel pump in 87-later TBI vehicles and the electric choke in the 80's pre-TBI vehicles. That switch works like I said previously where it is open when not pressurized and closed when oil pressure is applied. The single prong switch is just providing a switched continuity to ground through itself and drives the warning light. That one works the way you stated and is the one I linked to in my earlier post.

 

[Hamgrease]

I don’t have a switch it’s the same sensor that’s on my 87 for the gauge, I know the difference between the two they are completely different but that’s a good point,the gauge is maxed out no matter what I do I can unplug the sensor move the needle to 0 manually turn on the ignition lock to power it up it maxes out same thing with it connected to the sensor or not. It’s got a great harness so I know it’s not bad wiring from the cluster to the oil sender

 

[Hamgrease]

It’s a single wire sender

 

[Hamgrease]

The gauge also stays way past the max psi when I turn off the switch

 

[Hamgrease]

I appreciate all of the advice guys, it has a gauge only no warning light for the oil pressure

 

[duece1951]

Gauge maxes out without engine running, and stays there when running. Every other gauge works properly. I’ve checked the prongs top left 12v top right 8v, bottom center ground, checked top left to where it plugs into the back of the cluster 8v, when it passes through the bulkhead at the firewall it goes to over 11v . I completely replaced both tan wires from the cluster plug in to bulkhead and from bulkhead to oil pressure sensor, ohms reading 0 checking the sensor itself. I even bought a new gauge and tried it doing the same thing. I’m stumped. I put brand new grounds from frame to engine, engine to body both battery cables are new I made sure they were grounded to bare metal even the headlight ground. Both fuel tank grounds are good or they wouldn’t be working when I switch tanks. Anything else I could have missed?

Mine did that exact same thing. I ended up running a new wire and soldered it on the top right prong where the pressure gauge hooks into the dashboard. My brown wire was gone so had no choice. 1984 GMC off the oil pressure sending unit behind the carb.