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Could a Bad Alternator Keep Blowing Fuses?

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  • Could a Bad Alternator Keep Blowing Fuses?

    So, I've been trying to figure out why my 7.5a fuse (under the hood) for the alternator keeps blowing. As you can guess I'm not getting a charge on my battery that is new today (12.3v when running) and I cannot test the alternator because the fuse keeps blowing. There was a short with a small fire a few months ago, from a loose amp wire on the positive terminal (installed be the previous owner) which I quickly put out. I did find today, that the positive cable was crispy and had melted against the negative cable below the battery so I pulled them apart and wrapped them with electrical tape. I also cut back the positive cable and reinstalled the terminal. I have been driving it everyday for about 3 months since the incident with no issues. I recently changed the plugs and wires that fixed a stumble I had at idle about two days ago. Also, I have the driver's door panel off waiting on a window regulator. I read somewhere that fog lights are somehow related the the alternator fuse? The fog lights do not work, but I do see a separate fog light fuse (20a) and it is fine. I checked the megafuse and it checks out. I looked at the wiring from the alternator and all looks good. I went through 5 fuses today trying to figure this out. I just don't see how a bad alternator would blow a fuse the second I put it in? Voltage regulator in the alternator? Also, the previous owner had the alternator replaced about three years ago. Any ideas on this headache of a problem would be greatly appreciated! Thanks! 1999 SE 2.5 mtx.

  • #2
    If you haven't already ........ disconnect all the wires from the alternator and try another fuse ....G
    ST24. LPG, 2001 ST200 motor, 65mm P&P'd TB, 80mm MAF, headers, lowered, sway bars and strut braces, 300/278mm brakes, 3.51 FD 3.0L tranny, Torsen, Fidanza.... Vortech nearly completed.

    WANTED; Custom gauge guru for ST200 overlay job... pm me..

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    • #3
      The voltage sensing wire for the alternator also uses the same fuse as the fog lamps. Could be an issue with the fog lamps that are causing the issue.
      - 12 Focus SE
      - 99 Contour SeVT <- 3L/NPG Turbo
      - 2k Contour SVT - #2137

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      • #4
        Originally posted by gorman View Post
        If you haven't already ........ disconnect all the wires from the alternator and try another fuse ....G
        Will try this tomorrow after I buy a large box of fuses ;/

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        • #5
          Originally posted by BrApple View Post
          The voltage sensing wire for the alternator also uses the same fuse as the fog lamps. Could be an issue with the fog lamps that are causing the issue.

          I did disconnect both fog lights and still blew the alternator fuse. I looked at the fog light bulbs today and both were blown. Got two new bulbs...will try hooking up one tomorrow to see what happens.

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          • #6
            The alt itself could be shorted in any number of ways. The VR is indeed inside the alt and that should be the PCM controlled alt I believe.

            Simply retaping up melted cable is pretty much asking for it, the cable will have likely increased whoppingly in resistance and that alone might blow your fuses.

            Personally I'm finding issue with 'today' finding positive and negative cables melted together yet you drove it for 3 months like that. Likely why you are at where you are today....................

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            • #7
              Originally posted by amc49 View Post
              The alt itself could be shorted in any number of ways. The VR is indeed inside the alt and that should be the PCM controlled alt I believe.

              Simply retaping up melted cable is pretty much asking for it, the cable will have likely increased whoppingly in resistance and that alone might blow your fuses.

              Personally I'm finding issue with 'today' finding positive and negative cables melted together yet you drove it for 3 months like that. Likely why you are at where you are today....................
              Yeah, I wish I would have found it months ago too...The cables looked perfect but underneath the battery is where they were stuck together. I did check voltage on the positive cable behind the megafuse, and neg to frame it read the same as when connected directly to the battery. To me that says that my cables are good... But my electrical knowledge is minimal.

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              • #8
                Update, I hooked up new fog light bulbs and they work!

                Gorman, I disconnected all the wires to the alt. put in a fuse and it did NOT blow. So I am off to parts store for a new alt. Thank you! Not sure how much I'm looking forward to doing the replacement work...man it's packed up in there!!!

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                • #9
                  'But my electrical knowledge is minimal.'

                  Indeed, it is. Electricity will show full volts when there is no flow, that really has little to do with resistance in a big cable circuit. You are looking for mass amp flow ability not volts, the volts will drop as they hit resistance in mass. A meter doesn't show that unless you are measuring ohms.

                  You can cut the entire battery cable in half to get just one strand of it left and have the same 12 volts on the entire cable or the one strand. Give that some thought.

                  I'd make sure they throw that alt up on the tester before leaving the store, commonly many of them are bad right out of the box. When I used to sell them it was maybe 20% of them. They b-tch here about paying too much for rebuilding skills in the US but in no way do the Chinese rebuild any better than we did over here.

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                  • #10
                    ...... search the forum for 'replacing the alternator'........... you should find some tips to make it easier .... it can be a tough job the first time you do it


                    See if you can get the white plastic connector box on the back of the alternator tested ( the voltage regulator) ..the rest of the alternator maybe ok. ......G.
                    ST24. LPG, 2001 ST200 motor, 65mm P&P'd TB, 80mm MAF, headers, lowered, sway bars and strut braces, 300/278mm brakes, 3.51 FD 3.0L tranny, Torsen, Fidanza.... Vortech nearly completed.

                    WANTED; Custom gauge guru for ST200 overlay job... pm me..

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                    • #11
                      Amc49 is there a way I can test the cables? Thinking I will replace them just trying to figure out what to do where the positive goes to the starter...

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                      • #12
                        Originally posted by gorman View Post
                        ...... search the forum for 'replacing the alternator'........... you should find some tips to make it easier .... it can be a tough job the first time you do it


                        See if you can get the white plastic connector box on the back of the alternator tested ( the voltage regulator) ..the rest of the alternator maybe ok. ......G.
                        Thank you gorman for all your help!

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                        • #13
                          I ended up replacing my alternator TWICE, because the 1st one ended up screwing around with the PCM. The first one was overcharging at 15.6 volts, made it completely go in safe mode, PCM shut down the alt at higher RPM. Battery light was on bright at idle once it decided to charge the battery, but at higher rom, alt shut off, made the battery light go dim (according to Ford engineer, these cars activate the light bright at 14.9 volts and it shuts down the system at 15.8 volts and activates the light dimly at 12.7 volts).

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                          • #14
                            ... the P.C.M control circuitry wasn't adopted until 2000 over here, so I've never experienced that overvoltage situation

                            Originally posted by Contourado View Post

                            Thank you gorman for all your help!
                            you're welcome ...G
                            ST24. LPG, 2001 ST200 motor, 65mm P&P'd TB, 80mm MAF, headers, lowered, sway bars and strut braces, 300/278mm brakes, 3.51 FD 3.0L tranny, Torsen, Fidanza.... Vortech nearly completed.

                            WANTED; Custom gauge guru for ST200 overlay job... pm me..

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                            • #15
                              Originally posted by Contourado View Post
                              Amc49 is there a way I can test the cables? Thinking I will replace them just trying to figure out what to do where the positive goes to the starter...
                              You can test the cables to see if there is any connection to chassis ground, for instance disconnect the alt positive cable from the battery and the alternator. It should be "floating" now, and it should show no resistance to ground (resistance of infinity on a volt meter). You can also "megger" a wire, but the test equip to do that can get pricey. If there is a question of compromised insulation, then I would just run new copper wires with good insulation.
                              2k SVTC - Black / Praire Tan, blu_fuz ported 3.0L, 58k motor, 118k chassis

                              http://www.contour.org/ceg-vb/attach...chmentid=16333

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