@forestmods that is the oil pressure sensor.

Attached below is the R/R procedure for the coolant sensor for the USDM '03-'04 Forester. Perhaps that will help with your project.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]

 

The coolant temperature sensor is on the back passenger side of the coolant crossover pipe.
The diagram at this link can help 22630AA160 Genuine Subaru Sensor Assembly Temp

 

Thanks @2.5x_sleeper and @aaron, I've now replaced the coolant temperature sensor with an OEM replacement.

 

Hello there, I am replacing my sensor as I type. Since you have successfully manuvered the massive cluster of wiring harnesses blocking the sensor. Do you have any tips on how I can easily get this sensor out without getting any more gray hairs??? Any guidance is greatly appreciated. TIA

 

@Blondgma7 I used a crowfoot wrench to loosen and tighten the sensor.