1 – 2 pin E-fan instructions

NP 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 using the procedure below.
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.

  • For all efan harnesses 99-03+ perform the steps below.
  • Disconnect Negative battery cable.
  • Remove the 10mm nut from the alternator and attach the red power cables to the alternator.  This is the wiring with the 60amp J-case fuse and ¼” terminal.
  • Attach the black ground cables to one of the two bolts holding the red 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 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 a thin pick to remove the grey plastic cover on the pcm connector.  Push the pick into the pcm connector slot that the grey retaining tabs go into; then easily pry upward removing the grey cover.

Using a pick, remove the blue retainer by pushing the white securing clips on both sides and carefully pull up as you push in on the retaining clips.

  • For all efan harnesses 99-03+, insert the Blue efan harness pcm terminal into Blue pcm connector at location 42.   The pcm connector is numbered on the other side for reference.  Note:  be sure to put a small drop of lubricant on the terminal to avoid bending the terminal.

    For all 03+ efan harnesses insert the Green pcm wire into Green connector 33.

  • For all efan harnesses 99-02 perform this step.  For 03+ skip this step.
    Located below the red battery junction box, bolted to the alternator bracket, is a group of wires covered by loom.  Open the loom and locate the green wire (sometimes this wire is green w/white. Using pliers, crimp the provided red tap onto the green wire.
    If you are unsure of which green wire to tap into use a voltmeter to test for 12 volts on the green wire when the truck is running and the AC clutch is engaged.
  • The 3 relays attach to the black plastic PCM cover using the supplied screws.
  • Secure all wires with supplied wire ties.

Testing the Harness.

99-02 efan harness:  Applying Ground to the Blue efan harness wire will turn both efans on LOW speed
Applying 12 volts to the Green efan harness wire will turn one efan on HIGH speed.
Testing both of these wires will turn both efans on HIGH speed.

03+ efan 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.

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