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Thread: Big blue spark when connecting neg cable last on 66flh

  1. #1

    Default Big blue spark when connecting neg cable last on 66flh

    I am installing a new agm h12 battery in my 66flh, when i go to connect the neg cable last, i get a large blue spark, like the ign is on, i took my battery loose from my 68 flh just to make sure i was doing it right, no spark on the 68, any help from you electrical gurus would be greatly appreciated, cycle electrics has always been a weakness for me, thanks in advance, larry

  2. #2
    Join Date
    Oct 2011
    Posts
    479

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    Gotta multi meter?not a guru but set on ohms and read between the battery positive wire and ground with the battery disconnected and you will see an ohm reading.Find out what needs to be disconnected or turned off to get a zero,open reading,or look for a wire shorted to ground.Not a harley guy but I would probably start under the dash or wherever you were working last.
    Tom

  3. #3
    Join Date
    Mar 2008
    Location
    New Jersey
    Posts
    80

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    Larry,
    Information is always a good thing when trouble shooting electrical Gremlins. I have to ass u me you are dealing with a stock charging system. Does the arc remind you of flashing a field on a generator? It sounds like it to me. If you have a electro- mechanical (old style) voltage regulator, you may have a regulator with a stuck contact or if it is a new solid state one it may be faulty. Disconnect the field wire on the generator and if that solves the problem your regulator is probably the culprit. Again I am assuming you were only changing the battery and no other work was done. Also AGM batteries sometimes do not work well with old style charging systems. So keep a careful watch on the battery, it may not like an archaic charging system.

  4. #4

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    Lyle, exactly, looks like that arc, I will take a look at the regulator, it is the stock , old style, thanks so much, Larry

  5. #5

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    Lyle, I disconnected it, and it did not flash when I hooked the neg cable back up, but when I went to hook the reg back up it arced, is that ok or not, thanks Larry, I am just trying to determine which part is bad

  6. #6
    Join Date
    Jan 2006
    Location
    Menomonie, WI
    Posts
    1,265

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    I do not think that you should get any spark when you hook up the ground cable. I suspect that the cut-out stack part of your regulator is probably stuck shut. What the cut-out does is prevent battery voltage from flowing to ground thru the generator. It closes when generator voltage is higher than battery voltage (as when running) and opens when generator voltage falls below battery voltage (as when engine is stopped).

    Jerry

    Quote Originally Posted by Larry May View Post
    Lyle, exactly, looks like that arc, I will take a look at the regulator, it is the stock , old style, thanks so much, Larry

  7. #7
    Join Date
    Mar 2008
    Location
    New Jersey
    Posts
    80

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    Larry,
    It appears to be the regulator with a stuck contact. Over time the arcing sometimes causes the contacts to pit, not unlike your ignition points. You can try to clean them with piece of fine sandpaper do not use emery paper, the abrasive is metallic on emery. There is also a product called Plastones made specifically for electrical contact cleaning. I think I would just bite the bullet and replace the regulator. I replaced the one on my Pan a few years ago, probably made in China, and the original Delco cover went right on.

  8. #8

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    Thanks everyone, looks like a new regulator is in store

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