Affirmative - knock sensor.
The drawing in my 2002 factory Shop Manual is not that clear but it looks like the KS for that year should be bolted to the side of the 3.0 block. However, the 2001 Ranger Wiring Manual shows no knock sensor at all on the 3.0 Ranger and a quick Google search seems to support that. Research! 3.0L owners with Knock Sensors!
I'm not sure what this all means but you could have a truck with a non-original engine and/or non-original harness.