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    Rattle57's Avatar
    Rattle57 Posts: 1, Reputation: 1
    New Member

    Jun 6, 2017, 09:35 AM
    Electrical problem
    I have a 2002 Road King. While driving my headlight dims and then gets bright again. Ill so the check engine light stays on for a few seconds after starting the engine. I put a new battery in last fall. Seams like a charging problem?
    ma0641's Avatar
    ma0641 Posts: 15,681, Reputation: 1012
    Uber Member

    Jun 6, 2017, 11:24 AM
    Sounds like a voltage regulator issue. Fairly common on motorcycles, see the light fluctuating all the time.
    smoothy's Avatar
    smoothy Posts: 25,495, Reputation: 2853
    Uber Member

    Jun 6, 2017, 02:04 PM
    I seem to remember some of the older alternator models having issues with the stator, I have never dealt with this problem...

    I lifted this off another forum.

    Step 1. Normally, you'd first load test the battery.

    Start the engine and measure DC Volts across the battery terminals, the regulator should be putting out 14.3 - 14.7 vdc at 3600 rpm and 75 degrees F.

    Step 2. To check the regulator unplug it from the stator. Take a test light and clip it to the negative terminal of the battery and then touch first one pin and then the other on the plug that goes to the regulator. If you get even the slightest amount of light from the test light the regulator is toast.

    To do this with a meter which is more accurate: black lead to battery ground, red lead to each pin on the plug, start with the voltage scale higher than 12vdc and move voltage scale down in steps for each pin. Any voltage is a bad regulator.
    You may get battery voltage on all three pins on the newer 3 phase regulators.
    The no voltage is for older type regulators with diode indicating the diode is bad and the regulator needs replacing.

    Step 3. On the other part of the disconnected regulator plug. Set the multimeter for Ohms x1 scale and measure for resistance across the pins of the stator. You should read something around 0.1 to 0.2 ohms for the TC88 32 amp system.

    Step 4. Then check for continuity between each pin on the plug and frame/engine ground. The meter needle should not move (infinite resistance)(digitals will show infinite resistance) if the meter needle does move (indicating continuity)(digitals will show some resistance), recheck very carefully. If the meter still shows continuity to ground the stator is shorted (bad).

    Step 5. Set the meter to read A/C volts higher than 30 volts (the scale setting for voltage should always be higher than the highest voltage you expect or you may fry the meter). Start the bike, and measure from one pin to the other on the plug (DO NOT cross the multimeter probes! - touch them to each other). You should read roughly 16-20 vac per 1,000 rpm.

    Step 6. If the battery was good under load test, if the stator is NOT shorted to ground, and the stator is putting out A/C voltage, then the regulator is bad (most likely even if if passed step 2).

    Generally the following is true:
    Check your owners/service manual for the system amp output for your bike.
    22 amp system produces about 19-26 vac per 1,000 rpm, stator resistance is about 0.2 to 0.4 ohms.
    32 amp system produces about 16-20 vac per 1,000 rpm, stator resistance is about 0.1 to 0.2 ohms.
    45 amp system produces about 19-26 vac per 1,000 rpm, stator resistance is about 0.1 to 0.2 ohms.

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