When I try to start it, a relay under the seat chatters. Pull start is fine. 2004 Big Bear 400. It seems that the battery is not charging, but when I put on a charger it hold 12+ VDC. Lights get very dim in a short while.
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Is that relay bad and is it part of the charging circuit?
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Where is the alternator or equivalent on this engine?
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New to ATV's but not to engines.

mwap .. welcome to the frontier... They have a stator that keeeps the batt charged . It sounds to me that you have either a low battery or bad connection.Remove your cables and clean and charge the battery and try again ...if battery will not hold a charge it may have a shorted cell.If you start the bike with pull rope ,check at the battery terminals with a voltmeter and the engine revved up a little , you should have 12.8 to 14.2 or so volts if your voltage is way high you could have a bad battery or regulator.