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Thread: R90/6 electrical gremlins

  1. #1

    R90/6 electrical gremlins

    Lately my 74 R90/ 6 generator light has been flickering on when im going down the road, not when idleing but when im under power going down the road, it actually goes out when im setting at a light. Tonight after my sons baseball game it wouldnt start because of what sounded like a low battery. Probably an old question but what is the likely problem?

    Thanks Greg

  2. #2

    Start with the easy stuff

    Check and clean all connections under the front cover. Remove the bat- connection before you start removing the front cover. Eyeball the brushes to make sure they are riding securely on the alt. rotor, and not gunked up. Next check and clean all connections on the relays under the tank. There are other threads on the topic. Search the airhead archive here, and on the following sites:,, and DO NOT pull the front cover without isolating the battery. It is essential to have a fully charged battery if you resort to taking readings. If the connection thing succeds, let us know. If not, we'll have to dig deeper. There are lots of knowledgeable people on this forum. I am confident you will succeed.

  3. #3
    Loose Cannon flash412's Avatar
    Join Date
    Apr 2003
    Northern Colorado
    Worn alternator brushes are a likely candidate.

    At idle, the engine runs smoothly and they stay in contact with the slip rings on the rotor. While riding, bumps in the road cause them to lose contact because the brushes are too short for the springs to have enouth tension to keep them pushed toward the rotor hard enough to maintain contact with the slip rings.

    You might want to take a pink pencil eraser and clean the slip rings, too.
    Last edited by flash412; 05-12-2005 at 12:18 PM.
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  4. #4
    Rally Rat boofer's Avatar
    Join Date
    Oct 2004
    Landstad, Wiscowson
    My R90/6 had similar problem, diode board was the culprit. Can't say the light went out at idle however.


  5. #5
    I had the exact same problem with my 90/6 when I first got it. After a lot of searching it turned out to be one brush. There is a coil spring that pushes down on the brush, it needs to have a full turn of pre-tension. One of the brushes had the spring installed with too little tension, that caused the problem.


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