If the oil temp is showing a high temperature with the sensor unplugged, I suspect the oil temp signal wire is shorted to ground.
To verify the wiring:
With the sensor unplugged and ignition on (and engine not running) check for voltages at the harness:
• One wire should have about 5 volts from ground.
• The other wire should have 0 volts (or close it) from ground.
To verify the sensor:
• measure the resistance across it:
• at 10C / 50F it should be around 3600 - 3900 ohms
• at 20C / 68F it should be around 2100- 2900 ohms
Often, when troubleshooting it is good to know what the correct/working voltages should be.
Using a multimeter, measure the voltage across the oil temp sensor, with the ignition on but without the engine running. Use the table below to verify correct operation - or just look at your gauge
Temperature & voltage table for our oil temp sensor (and the coolant sensor, they are the same part)
Temp C/F ---- Voltage
11C / 52F ---- 3.84 volts
16C / 61F ---- 3.68 volts
24C / 75F ---- 3.36 volts
Good luck!