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GM Truck e-fan harness installation

GM Truck e-fan harness

Your PCM must be programmed for electric fans to operate correctly.

*NOTICE: If you receive the incorrect harness, email Nelson Performance. Any harnesses that are modified or installed will not be replaced.

Before emailing NP for tech assistance, test your harness!
If the harness works as described below, the harness is functioning correctly and the installation is causing the issue.
OR, your PCM is not calibrated correctly for efan operation.

Testing the Harness.  Applying Ground to the Blue efan harness wire will turn both efans on LOW speed.   Applying ground to both the Blue and Green wires will turn both efans on HIGH speed.

  • Disconnect Negative battery cable.
  • The PCM is located next to the battery and is covered with a black plastic shield. Remove the shield by pulling the sides outward to clear the retaining tabs.
  • Using a large screwdriver, unfasten the large metal clip securing the PCM.
  • Then pull up on the plastic retaining tab, you can now release the PCM from its mount.
  • Using a 7mm socket loosen the two securing bolts holding the PCM connectors.
  • Once the connectors are removed, use pliers to remove the grey plastic covering from the PCM connector.
  • Using a pick, remove the green and blue retainers by pushing the white securing clip on both sides.
  • For single PCM terminal e-fan harnesses, skip to Step 9
  • The PCM connector is numbered. Be sure to lightly lubricate the PCM terminals, it allows the terminals to be easily pushed into the rubber seal.
  • The terminal must push all the way thru and click into place.  Be sure all terminals are evenly pushed through the connector.

  • Blue Connector PIN 42 – Blue wire

  • Green/Red Connector PIN 33 – Green wire


  • Located between the junction box and ground mounting point is a group of wires covered by loom.  Open the loom and locate the green wire. Locate the green wire on the fan harness and attach it to the red tap.  Using pliers, crimp the provided red tap to the green wire. 
    After installation, a voltmeter may be used to test for 12 volts when the truck is running and the AC clutch is engaged.
  • Remove the 10mm nut from the alternator and attach the two red power cables to the alternator.
  • Attach the ground cables to one of the two bolts holding the junction box to the alternator bracket. The ground cables need to be between the alternator bracket and junction box mount to ensure a good ground.
  • The relays attach to the black plastic PCM cover using the supplied screws.
  • Secure all wires with supplied wire ties.


Fan Operation stock thermostat:

Low speed ON:  200 /  OFF:  198
High speed ON: 210 /  OFF:  206
For 180deg thermostats, values are roughly 4degs lower than a stock stat.Fan Operation 160deg thermostat:

Low speed ON:  182  /  OFF:  180
High speed ON: 188 /   OFF:  185