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  • Bad new alternator ?

    Just replaced the alt on my 2000 Caddy .... New battery ... Voltage was 11.9 or so while running ... Checked the connections and the fuses ..All seemed good ..
    Started and rechecked ...Voltage was at 14.1 for a few seconds then went down to below 12 again ... Could I have a bad alternator ...The box it came in was pretty beat up if that means anything ... Voltage regulator maybe ? I know why I'm not a mechanic ...
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  • #2
    Sam, how are you reading the voltage? If by a meter on the dash, I would get a hand held volt meter and check it.
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    • #3
      Hand held meter at the battery
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      • #4
        If it's a " remanufactured in Mexico" like from Autozone or similar parts store then it may be bad already....same with their starters....This from my first hand experience.....

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        • #5
          It was not a re- manufactured one .. I almost got one but decided on new one .. Got it from Advanced
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          • #6
            Check at the connections on the alternator, to see what it is actually putting out, sounds like you might have got a bad one anyway, it happens.

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            • #7
              I was gunna check it at the alt MTb when I got home today but somehow the brand new battery drained down to 9.8 volts last night ..
              I think it was the radio . For some reason it will not turn off unless you open and close the passenger side door .
              I put the battery on charge and try again tomorrow ..
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              • #8
                Originally posted by sphelps View Post
                I was gunna check it at the alt MTb when I got home today but somehow the brand new battery drained down to 9.8 volts last night ..
                I think it was the radio . For some reason it will not turn off unless you open and close the passenger side door .
                I put the battery on charge and try again tomorrow ..
                Sounds like you have more issues than just an alternator.

                I do know that regulator output is computer controlled. It needs to sense that it needs to charge before it excites the alternator.

                The radio should turn off after several minutes or when either front door is opened. There is a wiring loom by the bottom hinge.
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                • #9
                  How many wires go to your alternator besides the one going to the battery?

                  If only 2, one connects to your instrument cluster and one gets controlled by PCM. It's the one that controls your field. If the PCM output is faulty, the alternator will not get energized.

                  If you have more than 2, your PCM has an on/off and a duty cycle control going to the alternator.
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                  • #10
                    Looks like just one small wire that clips in other than the large one to the battery ..
                    Been busy and getting home late so I have not had a chance to fool with it ... I have a family mechanic coming out this weekend to help figure it out ... He has a diagnostic tool to check things out ..
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                    • #11
                      Connect your meter between battery negative and disconnected battery cable and read it while pulling fuses ..That will show which circuit is draining the battery
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                      • #12
                        What do I set the meter on and what am I looking for to know if there is a drain .
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                        • #13
                          Forgot to mention it was a bad alt .
                          Terminal post was broken is what they said and gave me a replacement .
                          It did seem a little loose when I installed it to start with . It was like that right out of the box .
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                          • #14
                            Originally posted by sphelps View Post
                            What do I set the meter on and what am I looking for to know if there is a drain .
                            Did you even say you had a drain?

                            Measure in Amps mode on your meter...I hook the meter between the negative battery post and the neg battery cable. You have to have doors closed and wait around 15 minutes because various CPUs in the car will go to sleep after not having any inputs for awhile. Was doing this very thing last night with my mom's 2007 Buick that is draining the battery over a week. After closing the doors, it is drawing 5A and eventually goes down to 120mA. Pulling the cig lighter fuse, it goes down to 0 so something on the cig lighter circuit is drawing power.
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                            2006 Sun Tracker Party Barge 21
                            Mercury 90 4-Stroke FI
                            "Common sense is not very common"
                            "Failing to prepare is preparing to fail." -- John Wooden

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                            • #15
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                              Yes Bruce I had installed a new battery and over night it had drained down a lot .
                              It may have been the radio not shutting off idk....
                              So if it zero's out after the doors have been shut for a while there should be no drain .
                              I'll try that and see what happens .
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