sounds like you need to test the wires from ecu to sensor. make sure the wire hasnt be crushed.

when you say jumper harness do you mean conversion harness?
2000 ecu is obd2, with chip and conversion harness it changes it to obd1, that conversion harness could be bad, they arent really built that well, its a solid connector plug with pins at both ends thats was originally designed for circuit board applications. each terminal gets the 90 degree elbow cut off and wire soldered to it. the wire could just be broken free or not getting a good connection.