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Headlights dim all of a sudden

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  1. #1
    Member Modelman's Avatar
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    Headlights dim all of a sudden

    Hello. I have put about 150 miles on my SR Cafe racer now suddenly my lights have gone very dim, horn and indicators stopped working. I have a battery eliminator but everything else is stock. The intensity of the lights is the same at all engine speeds. I'm only getting a couple of volts at the BE any at any revs. I disconnected the BE and still only 2 volts.
    I connected a 12v battery and all lights etc working normally.
    This is what I have tried.
    Check the generator coil resistances at the plug-seemed ok. Started engine and getting about 40v at fast idle rising to 60v+ At 3000rpm. got same voltages at the rectifier plug.
    I checked the rectifier getting continuity one way, nothing the other as per the manual. Strangely the beeper didn't sound on my meter but the display lit up.
    Plugged rectifier back in , started up and poked my meter into the red, brown and black wires coming out of the rectifier and would have expected a decent voltage but only getting a couple of volts- is my( brand new) rectifier toast even though it seems to pass the continuity test. I am crap at electrics and all out of ideas.
    Thanks for any help you can offer.
    Pete

  2. #2
    Senior Member YucA's Avatar
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    Stupid question, but is the "new" rectifier a combo regulator/rectifier? You said nothing about testing a regulator. Even with a capacitor in place of the battery (BE are just big caps), you still need to regulate the voltage after the rectifier converts it to DC.

    So, if your new rectifier is a combo unit, it probably cooked itself if you are seeing AC in and nothing out... Or, you still have to test more electronics (regulator), and maybe its just your new rec. OR, you ran the electrical system with no regulator and you probably fried the cap (BE).

  3. #3
    Banned Witworth's Avatar
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    By "new regulator rectifier" do you mean a stock Yamaha Shindengen one or some cheap pattern copy?. I have never had a OEM one fail in 100's of thousands of miles. I must have owned twenty of them, with no issues in testing, or in use.

    BTW, your diagnostics make about zero sense to me, and I've done M/C electrics professionally for years. Go buy a Haynes SR manual to help you.

    Danger, is my business."
    Last edited by Witworth; 03-30-2015 at 02:08 PM.

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  5. #4
    Member Modelman's Avatar
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    Yep it's a not so cheap copy rectifier/ regulator, borrowed a friends one tonight and it's behaving perfectly, so I must have a dud one. Don't understand Mr Witworth's comment about it making no sense -checked charging voltage at the 'battery' end then gen coil resistance then output voltage of each phase both at generator plug and other end where it connects to the the rect/reg then DC output from rect/reg, verified I had good continuity through all wiring by connecting a 12v battery, seems pretty logical to my inexperienced electrical prowess , please can Mr W help me by explaining what I did wrong, thank you. I do have a Haynes, got one for every vehicle I ever owned ( except my late Civic- they don't do one), they are ok but not as good as some the factory manuals I have. The one I had for my RC30 was amazing at the level of detail. Haynes certainly very limited in helping me sort this problem apart from giving me the resistance figures and how to check the diodes in the rect/ reg, nothing about checking the regulator part. Anyway will be ordering new unit from Speedshop. As I said I am crap at electrics just tried to figure it out by a process of elimination.
    Last edited by Modelman; 03-30-2015 at 05:37 PM.

  6. #5
    Senior Member hillsy's Avatar
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    You've just done a proper diagnostic by swapping out the "suspect" part and using a known good one. Depending on the reg/rec unit there are different tests than just continuity (diode test, etc).

    BTW - lots of things don't make sense to witworth.

  7. #6
    Banned Witworth's Avatar
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    Well, by your own admission, you are bad at doing electrics.

    And I, with my professional perspective, you're a bit crap at describing your efforts.

    Problem solved by playing swapsies, and its all good.

    Danger, is my business."

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