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Discussion Starter · #1 ·
My 3910 alternator light stays on except occasionally it will flicker an go out
for 5 min or so then come back on . I have checked the voltage with it running an it shows 12.55 to 13.99 I don't mean it flucuates that is just the different readings I have sean when checking it . How do I tell if its the regulator or the alternator ? My battery is staying up enough to start the tractor although I don't know if it would if I were useing the lights . I did turn them on while checking voltage an thats when I got that 12.55 reading .
Just thought one of you guys might help me trouble shoot it before I pull it .

Thanks George
 

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Best thing to do is pull it and take it in for a free test at your local parts place, 12.55 ain't charging your battery. When the alternator is charging you should read about 14v at the battery.
 

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Old 'n Cheap
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Might be a good idea to clean all the related electrical connections. Make sure you have good grounds. If it has ever been repainted it may be grounding, or trying to, through a thin layer of paint. If never painted it may be trying to ground through a little rust. Check for frayed wires at connection points.
 

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Discussion Starter · #5 ·
All good suggestions ryork took it an regulator over to a friends shop he had a tester to check the regulator it was bad . The alternator check good 14.5 volts . But I also got a little education on how to check the alternator while its on the tractor . Most of the time I just go to the battery post with my volt meter . But if the reading there is low the question becomes which is it Alt or REG . Well I had tryed that going from the hot post on the ALT to ground but since the bad regulator was still hooked up it was not letting
the Alt put out full voltage . So he showed me which wire to unplug which is at the top
center then he had a 12 volt light bulb with two alagator clips he went from that hot post to the post that the regulator hooked too an bingo the voltage came up . That is what I was trying to find out how to do before I pulled it . I guess it has to since a demand before it will energize .
 

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Thanks Travelingman for sharing that bit of info. I'm sure if I can remember it when I need it I will be able to use that some day. My brain seems to take in a lot more info than it lets out...
 
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