Confirm the Gauge is OK by Using an External Signal
Most issues are due to incorrect wiring or sender hookup. If you have access to a 47 ohm - 100 ohm resistor you can easily verify the gauge is OK as follows:
With power to the gauge and a resistor across the signal input and ground you will see the pointer move to to the corresponding dial position.
- Disconnect the signal wire from the gauge.
- Install the resistor between the signal and ground connections on the gauge.
- Connect 12V Power and Ground connections to the gauge.
If you do not have access to a resistor but do have another working fuel level or temp gauge you can use the power, ground and signal connections from the known good gauge on the oil pressure gauge to verify that the oil pressure gauge is OK. Note, the pointer will move according to the ohm output from the sender you are using to test the gauge.
- For gauges with Type 1 or Type 2 sender: 50 ohms ~ 45 PSI, 100 ohms ~ 90 PSI.
- For gauges with Type 3 sender: 50 ohms ~ 90 PSI, 100 ohms ~ 70 PSI.
Confirm the Type of Sending Unit
There are three types of oil pressure sending units.
- Type 1 has no label. This sender was supplied with most SCX gauges shipped before 2015.
- Type 2 has a yellow label stating "WK = Ground". This type of sender is supplied with Comp II gauges.
- Type 3 is silver in color and has a white label stating "240-33 OHM (0-100 PSI)". This sender is supplied with most SCX gauges shipped after Jan 1, 2015.
Verify Wiring and Common Ground
Verify your wiring is good and that the gauge and sender both have a good common ground (ground both to the same place on the chassis).
If you have a Type 1 sender (no label) make sure you have not connected anything to the WK terminal. Verify the sending unit has a good ground connection on the body of the sender. If in doubt, install a metal clamp around the sender body and run a wire from the clamp to a good ground location on the vehicle chassis.
Verify Ohm Signal from Sending Unit
Turn your vehicle on and let it idle. Disconnect the gauge signal wire from the sender and check the ohms output with a multi-meter as follows:
- For Type 1 sender, the G terminal is the signal and the body of the sender is ground.
- For Type 2 sender, the G terminal is the signal and the WK terminal is the ground.
- For Type 3 sender, - terminal is the ground and S terminal is the signal.
Compare the ohms output with the expected ohm output. At idle (typically 20-30 PSI) you should see 20-40 ohms output from the sender. If the sender is not reading as expected contact us for a replacement.
Verify Ohm Signal at the Gauge
Reconnect the gauge signal wire to your sender, disconnect the signal wire from the gauge and check the ohms between the signal wire and gauge ground wire (signal wire needs to be disconnected from the gauge). The ohm reading should be the same as you measured at the sender. If it is not, then you will need to check your wiring (verify common ground etc.).
Verify the Gauge
Back to FAQs
Check the SCX or Comp II pressure/ohm data (found here) and confirm that the gauge is reading at the expected pressure for the ohms reading at the gauge. Example: at 20-40 ohms, the SCX and Comp II oil pressure gauge should read 20-30 PSI. You should see the pressure rise and fall in synch with the engine RPM's. If the gauge is not reading as expected contact us to return your gauge for checking/replacement.
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