Take a resistence reading of the THA signal wire, between the ecu plug and afm plug with both ends disconnected.
Take a short test of this wire also, disconnect both plugs and test for continuity to the body. If you have continuity there is a short so take a resistence reading to ground. The lesser resistence reading should be closer to the short, if it were a printed circuit board atleast this is a little complicated in an vehicle.
Do the harness resistance checks (FSM ecu section). Anything that is out of spec in this test is either a bad sensor or bad wire.
There is great big long post on testing wires here
And of course your meter might be out of calibration, test it against another(or two or three). We're not launching rockets to mars, it doesn't have to be spot on just in the ball park and give consistent readings.
Proper (eg clean), good (eg sharp) probes, well seated and no fingers in the reading.
You can take the wiring and ecu out of the equation. Disconnect the afm plug and supply 12v to Vb and ground on E2.. Er scratch that!
Look at the diagram/schematic for the AFM notice that the THA sensor has one side connected to ground and the other to the ECU. What this means is the voltage you see on the THA at the ecu is comeing FROM the ecu! There is either a) a voltage supply problem to the ecu B) the ecu is damaged.
Again, Voltage supply to the ECU or the ECU is damaged.
So swap in the new un cut/mangled harness. Important that you don't plug the new ecu into the mangled harness
! You might damage it also then your new harness won't help untill you put in a third ecu.