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  1. #1
    CB750 New Member Thoruss's Avatar
    Join Date
    May 2020

    When headlight is on, bike no longer charges...

    Hi there, I'm new here but I've owned my bike a few years now (76 cb750f)... When I bought it it wasn't charging. So I've been through most of the electrical.... Got it charging but as soon as the headlight is on it won't supply amperage to the regulator... Voltage is present but no amperage.... To me that means resistance in the circuit. I tested resistance in the circuit with the ignition in on and off/on to on. Found. 3 ohms which should be a good circuit. I load tested (but forgot to test voltage across the bulb) but it seemed to be at full brightness... Wasn't dim that's for sure.. But this is all with the light unplugged.

    I wired in a relay thinking that it would provide a better reference voltage to the regulator than through all the switches (it started over charging after I got it to charge) which as far as I'm awair is because it wasn't getting proper voltage reading from the battery. Even with the relay on black with the headlight put in... It doesn't have enough amperage to activate the relay. Without the headlight plugged in the relay works and it charges properly.

    Any advise for me from the experiences guys? I'm a mechanic of 10 years and generally I specialize in electrical. I don't have a full wiring diagram however.

    Any help or ideas would be appreciated.


  2. #2
    CB750 Addict Medyo Bastos's Avatar
    Join Date
    Oct 2012
    Mid South
    Have you measured resistance on the conductors to your headlight?

    Sent from my iPhone using Tapatalk

  3. #3
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Fort Worth TX.
    Your regulator and rectifier both have problems if they are separate units. The only way you can get true overcharging is by regulator loss of control. The rectifier if diodes are damaged will only put out part charging, enough to seem to work but throw headlight on and it then is not enough, the headlight output soaks most of it up as it is not the full amount.

    Inserting another relay in there is a mistake, it only complicates things further. The regulator itself is a relay.

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