Corrosion and physical damage are the most common reasons to replace an engine control module wiring harness. Exposure to moisture slowly corrodes the wire's harness and causes the ECM to shut down the vehicle's engine. The wire connecting the fuel solenoid to the harness is another common failure point.
A crack or break in one of the wires also prevents the ECM from operating correctly. TUsing a voltmeter to check the current at the point where the wires enter the harness makes it possible to find potential problems in the ECM wiring harness. If the reading is six or lower, the ECM is not getting sufficient power. A vehicle that does not restart after running well may also have problems with the connection to the ECM.