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Thread: Bulb Issues (Headlight)

  1. #1

    Bulb Issues (Headlight)

    Well, the R100 Cafe bike has been running well with the new Mikuni VM38s on it. I do now have an electrical issue/question. The headlight on my 1984 R100 remains stock, as does the wiring harness, except there is no volt meter on it. (I need to install one). I have recently started to burn out the Quartz halogen headlight bulb. Last night, I took a few spare ones and the bulbs filaments fried in seconds.

    It happens when I twist the throttle. There appears to be a surge in the light intensity and then, the bulb burns out. I switch to highbeam, same thing happens. So there is a pattern. I was thinking maybe the voltage regulator is on the fritz, but no other electrical problems appear to be happening. (This has been also suggested in previous threads) Any guidance is appreciated.

    Last edited by pedrocasper; 06-20-2008 at 01:27 PM.

  2. #2
    Registered User skiteach's Avatar
    Join Date
    Dec 2006
    Woodbury Ct
    Voltage Regulator! Check volts at battery at higher rpm, should not excede 14.5v. VR under gas tank, headlamp bulbs are acting as fuse, or indicator.
    '73 R75/5
    Never had a bad day skiing!

  3. #3
    Yup! I've been thru this myself. In fact I'll tell you how it came to me. I used to have 60's British bikes, and on a ride home from Indiana, I got to wondering about why I was popping headlights on my R75/5. I got to thinking about my old BSA and how an output over 13v would overheat and fry the Zener diode and then it hit me; an un-regulated charging output (like when I super-revved the BSA) would smoke the diode and then I'd be killing headlights. The same is true on our BMW's, if your'e wasting headlights, your regulator has ceased to regulate. The Lucas system used a single diode for a regulator as compared to a relay like Bosch, but the effect is exactly the same.

    Oh, and a failed regulator on the Bosch system will not light up the dis-charge light because the system is over-charging, not dis-charging.

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