[macgyver]

It looks like they got a little smarter with that location, I think mine is hidden because it might be one of the first newell's with a computer !! Thanks

I think you said yours has an override button.
Is it a Detroit?
I know a little about Big trucks and the Detroit engines & have worked on several of my own.
Turn the ignition on, push the override button and the codes will start flashing.
If the reservoir is full, take a paper clip & make a U with it , unplug the sensor and stick the paper clip in the plug.
If it runs then it is a bad sensor.
I can post a code chart if anyone needs one.

There are no problems right now after I topped up the rad but I am just trying to locate the computer terminal for future use ! Someone has already posted a code chart earlier in this thread.I will try that override button to see if it works, thanks