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Thread: Red "Gen" Light on R75/6

  1. #1
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    Red "Gen" Light on R75/6

    4 of the last 5 times I have ridden my '75 R75/6 during the last week, the Red "GEN" Light between Nuetral and Oil is glowing. While riding, it stays on, although pretty dim. When I am idling at a stop, it burns full force. This is confusing me for a few reasons. First, for the last year or so, this light never even came on, even when I turned the ignition on. According to my mechanic, that made no sense for some reason or another, plus all my other display lights were working properly. Second, after riding home yesterday from a 20 minute commute, 4 hours later I hooked up the battery tender and within 30 minutes I was getting a green light indicating full charge. I don't know much mechanically/electrically, but it would seem to me that if the battery were on it's way out, it wouldn't recharge so easily? I only used the charger to see how long it would take. Prior to that, I hadn't been charging the battery regulary, and things seemed fine. Then last Friday, the light comes on. To add to this, on the ride to work yesterday the light didn't come on, but reappeared on the ride home, and again this morning.

    The bike seems to be riding normally.

    Does it sound like I have reason to be concerned, or is my board just acting up? Any suggestions would be appreciated.
    By the way, the battery (made by BMW) is approx 18 months old, and the water level is good.

  2. #2
    Loose Cannon flash412's Avatar
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    Re: Red "Gen" Light on R75/6

    What happens when you put a voltmeter on the battery? What does it read with the motor stopped, at idle, at 1500 rpm and at 4000 rpm?

    Did you just get the bike out of winter hibernation?

  3. #3
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    No to the winter hybernation. I didn't ride this bike over the winter a whole lot (preferred the fairing of my K1100LT), but didn't let it sit for too long (3-4 weeks max.) without at least going out for 20-30 minute ride.
    Actually, I don't know if this would relate, but I road one day in mid-March in the rain. The next time I went to ride the bike it wouldn't start. It was turning over easy enough, but wouldn't fire. A few days later I tried again and after several attempts, I finally got it running. Before this, the bike would always start on the first try when dead cold in the mornings. Over the last week, it usually takes a few tries. Don't know if that helps.
    I plan on stopping by an auto store on the way home to get a volt reading on the battery. I will post the results later tonight or this evening.

  4. #4
    Focused kbasa's Avatar
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    Re: Red "Gen" Light on R75/6

    Originally posted by KAW
    4 of the last 5 times I have ridden my '75 R75/6 during the last week, the Red "GEN" Light between Nuetral and Oil is glowing. While riding, it stays on, although pretty dim.
    I'm going to suggest you take a look at your diode board. The half intensity gen light is the clue here.

    To check it, disconnect the battery (this is important!) and take the front cover off of your bike. It's the big oval one on the front of the motor. The diode board is a big square board about halfway up. They're mounted on rubber gizmos that sometimes get old and fail. They allow the board to short itself against the cover and will sometimes give you an intermittent half intensity gen light.

    Other times, they fail completely because they're old or whatever and they'll have big burnt spots on the circuit board.

    If your board is flopping around, you'll need to replace the mounts. They're not too difficult to do and they don't cost too much.

    I'd start there, your battery is probably fine.

    dave
    Dave Swider
    Marin County, CA

    Some bikes. Some with motors, some without.

  5. #5
    Loose Cannon flash412's Avatar
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    I once had the front cover of my 5/ get water in it from riding in a huge rainstorm. Caused all sorts of silly problems from hard starts to gen light acting oddly. Pull the front cover loose (after disconnecting the ground strap) and see if it is wet in there. If it isn't wet... THEN you can start to look at other things.

  6. #6
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    Voltmeter readings

    I stopped by an auto supply store on the ride home and here's what the readings say: Engine Off 12 v, with "load" 11v; Engine Idling 12v; @1500rpm 12v; @4000rpm 13.2v.

    The guy at the shop said "for a car battery, this would be a good sign." I assume the same applies to my bike?

    Funny how when something appears to be wrong, it's easy to assume the worst. After stopping by the auto shop I went tooling around on some back roads to take the long way home. I pulled over on the side of the road to grab something from my tankbag. As soon as I stopped the bike, the engine cutoff before I hit the kill switch. Not good.
    A moment later I start the bike - takes a few tries, but I breath a sigh of relief. 50 yards down the street, a few surges, and it cuts out. Not good. It won't restart. I'm all but ready to find the nearest house/phone, when I decide to try flipping the bike over to reserve, just in case. Mileage seemed a bit lower than what I typically recall for switching over. But, on the second try, she fires up and I ride the remaining 10 miles to the gas station and home flawlessly.

    I've read/heard similar stories from others, now I guess I have my own.

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