Oil pressure gauge not working

With the help of you guys I got my tachometer working. My next issue is the not working oil pressure gauge. I put 12 V across the Gauge worked. I have a new sending unit so I don’t think it’s that and I have continuity between the wire attached to the sending unit and a wire attached to the Gauge. Could hit have something to do with this unit?

If you take the wire attached to the sending unit and connect it to engine/body ground (-), what does your meter read ?
If you read full oil pressure, you know your sending unit is wrong.
If nothing, you know your wiring is faulty.
BTW, what are the fuel and temp meters reading? If off as well, it could be your voltage stabilator.

My recollection is that the oil gauge doesn’t use the voltage stabilizer.

Temperature gauge seems okay, fuel gauge seems questionable. There is a green wire that goes to the stabilizer

Just checked the wiring diagram. It looks like you’re correct. My bad. The oil pressure gauge and volt meter are both fed from the voltage regulator, but from the unregulated side.

Did your test and when i grounded the wire the gauge went to max. So that means the sending unit is bad, but it is new. Is that unusual?

sadly. No. Cue…Ray L.

Is there a way to test the instrument voltage regulator?

The voltage regulator uses the bimetallic strip with a heater wrapped around it to create an average of 10 V. If you put a voltmeter on the output you should read something that’s bouncing around. 0 V shows it’s dead and battery voltage also shows it’s dead. I built a solid-state one from a three terminal 10 V regulator. Only took me three tries but that’s another story. I finally determined that I voltage spikes at the input we’re frying the regulator. An LC filter on the input solved the voltage spike problem. It’s amazing what can show up on the car wires when you turn off the ignition switch.

I got a new sending unit and gauge still doesnt work. The gauge goes to full when I ground the wire from the oil pressure sending unit and there is 12 V to the gauge on the other terminal coming from the regulator I can’t figure out what else it could be. I do notice that when the white/brown wire from sending unit is grounded the gauge hesitates, jumps up and down and then goes to maximum. Could that mean that the sending unit doesnt send enough signal to get to make the gauge work?

To the best of my knowledge, the oil pressure gauge and sender basically represents two resistors dividing a voltage between them. One is variable (the sender) the other fixed (The gauge).
As an example, with two equal resistors connected between 12V and 0V, the point between the two resistors will have a voltage of half the 12V = 6V (if measured with a high impedance meter).
When the variable resistor is submitted to temperature change it will change it’s resistance.
When you say that there’s no change whether you use an old or new sender, my suspicion is that your gauge is faulty causing the voltage division between the two “resistors” to be working differently. It could give the symptoms you are describing.
I don’t know the inner resistance of the oil temp gauge, but will take the measurement if you tell me what your gauge’s resistance is.

Cheers … Ole

Have you continuity-tested the wire from the gauge?

Sounds like a possible open.

I tested continuity and i grounded the. wire at the sender which caused the gauge to go to maximum but it glitched at about 20 on the gauge abd then went to maximum

These oil pressure senders are notoriously inaccurate and many on this forum have complained that new reproductions either are faulty from the onset or soon fail. If you want a reliable and accurate solution, install a mechanical gauge. With one of those, you’ll even be able to watch you OP change with changes in engine speed. Another option is to get in line for one of Ray Livingston’s upgrades.

The sending unit is not a variable resistor. It’s a bimetallic strip and an electrical contact wrapped with a heater wire. As the Bellows moves in and out with oil pressure, the bimetallic strip is bent more or less. The heater wire heats the bimetallic enough to open open the contact. The higher the pressure the more heat( current) is required to open the contact. The same current runs through the gauge and will indicate a higher oil pressure. RubeGoldberg if I ever saw one

The current, when the points in the sender are closed, is more or less constant, and is determined by the resistance of the heating element wrapped around the bi-metal strip. What does change is the percentage of the time the points are closed, and, hence, the current is flowing. The sender acts as a pulse-width modulator, and effectively varies the average RMS voltage across the gauge. At higher pressure, the points are closed for a greater percentage of the time than they are at lower pressure. This means current flows through the gauge for a greater percentage of the time, so the heater in the gauge heats up further, moving the needle further to the right.

Ray L.

Thanks Bill and Ray for explaining the inner workings of the sender.
For troubleshooting purposes, the principle is a voltage division between the sender and gauge and my point is that with the tests that have been done so far, it’s time to check the gauge. I’d check the gauge if I was troubleshooting this problem.
With the comments about sender units being notoriously faulty out of the box, that is indeed a possibility.

What do you mean by “glitched” ?
Was it stuck for a short while ?

If the gauge does not move up smoothly all the way past the top marking when the sending unit wire is grounded, then there is a mechanical problem with the gauge itself.

Ray L.