From the J&P Cycles Blog Archive

We'd like to share some important information regarding Harley-Davidson full wave charging systems (covering 1970-2005 Touring, 1984-2007 XL, 1984-2000 Softail, 1991-2003 Dynas, all FXR’s)

Battery Test:

The battery needs to be a fully charged battery that has been load tested to ensure proper readings. If you are not working with a fully charged and functional battery, all other voltage tests will be incorrect. Most places like Auto Zone, Advance Auto, and Pep Boys will charge and test motorcycle batteries for free. Standing battery Voltage should be 12.5-13.2 DCV.

Charging System Voltage Test:

Start motorcycle, measure DC Volts across the battery terminals (you should have a reading of approximately 13.2-15 DC Volts).

Check Connections/Wires:

Inspect the regulator/stator plug, and check the battery terminals for connection/corrosion. If everything seems to be in order, move on to Number 4 below to determine if there’s a failed component.

Stator Checks/Rotor Check:

Each of the following tests isolate the stator & rotor. If AC Output test fails and resistance check, and Stator IB Test pass, then the rotor is at fault (pull primary covers and inspect rotor for damage).

AC Output Check:

  1. Unplug the regulator plug from the stator
  2. Start motorcycle and change voltmeter to AC volts.
  3. Probe both stator wires with your meter leads.
  4. The motorcycle should be putting out approximately 18-20 ACV per 1,000 rpm. (Reading will vary depending on system, check service manual specification)
  5. Generic Specs:
    22 amp system produces about 19-26 VAC per 1,000 rpm
    32 amp system produces about 16-20 VAC per 1,000 rpm
    45 amp system produces about 19-26 VAC per 1,000 rpm

Stator Resistance Check:

  1. Switch your multi-meter to Ohm x 1 scale.
  2. Probe each stator wire with meter leads and check resistance on meter.
  3. Resistance should be in the range of 0.1-0.5 Ohms. (Reading will vary depending on system, check service manual for specification)
  4. Generic Specs:
    22 amp system produces about 0.2 to 0.4 ohms
    32 amp system produces about 0.1 to 0.2 ohms
    45 amp system produces about 0.1 to 0.2 ohms

Stator IB test or Ground Check:

Switch your multi-meter to Ohm x 1 scale.

Probe each stator wire with your positive lead on the multi-meter and the negative to ground.

There should be no continuity to ground on either wire.

If there is continuity to ground, your stator is shorted to ground.

Regulator Test:

Each of the following tests isolates the regulator only, so if any of these tests fail, the regulator is at fault.

Identifying Wires:

  1. Battery Charge Lead - Wire going from regulator to battery positive.
  2. AC output leads- Wires coming from the stator to regulator.
  3. Ground- Wire from regulator to ground or regulator may be grounded via the physical bolting to chassis.
    Regulator Ground Test: Ensure the regulator body is grounded or grounding wire is fastened tight to a good ground (you should verify this by checking continuity from regulator body to chassis ground).
    Fwd/Reverse Bias Test/Diode Test: This check is testing the diode function to ensure it is regulating the AC current for the stator into DC Current.
  4. Switch multi-meter to Diode Scale.
  5. Place your multi-meter positive lead on each AC output wire.
  6. Place your multi-meter negative lead on the battery Charge wire.
  7. The meter should read voltage typically around .5 volts.
  8. Next, switch your multi meter leads putting the negative lead on the AC output wires and the positive lead on the Battery Charge Wire.
  9. The reading should be Infinite.
  10. With your meter on the same setting, place your multi-meter positive lead on the regulator ground wire or to the regulator directly, and then place your meter negative lead on the AC output leads.
  11. The meter should typically read around .5 volts.
  12. Next, switch your multi-meter leads putting the negative lead on the regulator ground and the positive lead on the AC output wires.
  13. The reading should be Infinite.
  14. Note: Below is a table to show the readings:
    Positive Lead Negative Lead Reading AC output 1 Battery charge lead Voltage AC output 2 Battery Charge Lead Voltage Battery charge lead AC output 1 ∞ Battery charge lead AC output 2 ∞ Ground AC output 1 Voltage Ground AC output 2 Voltage AC output 1 Ground ∞ AC output 2 Ground ∞ Replacement Components