69 GTX Green Alt-Reg Wire Burnt Up
#3188795
11/04/23 08:20 PM
11/04/23 08:20 PM
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Dads426
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Helping a friend diagnosis a problem with his 69 GTX, 440, 4-spd, stock restoration. Started it two weeks ago and ran fine. Started today and melted all the insulation on the green field wire to the old style voltage regulator. Could the regulator shorted the field to ground or is this an alternator problem? Thanks!
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Re: 69 GTX Green Alt-Reg Wire Burnt Up
[Re: Sniper]
#3188806
11/04/23 09:20 PM
11/04/23 09:20 PM
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Dads426
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No, harness is new with the black spiral tape on it. Melted the insulation off entire wire, but only ran for a few seconds, so other wires under the tape were not damaged. Will look at the alternator and see if the field grounded. When we checked the terminal on the regulator, it was grounded. Not sure if it’s a point type regulator or the a replacement electronic version. Will try disconnecting the regulator and see if the field is grounded.
2012 422 Allstars NSS Champion 2013 422 Allstars NSS Champion 2014 422 Allstars NSS Champion
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Re: 69 GTX Green Alt-Reg Wire Burnt Up
[Re: A12]
#3188819
11/04/23 10:39 PM
11/04/23 10:39 PM
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Dads426
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Went back and re-read your post and doesn't seem like anything on the output side was damaged or melted the insulation is that correct? Just the dark green wire?
Correct.
2012 422 Allstars NSS Champion 2013 422 Allstars NSS Champion 2014 422 Allstars NSS Champion
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Re: 69 GTX Green Alt-Reg Wire Burnt Up
[Re: dragon slayer]
#3188864
11/05/23 10:16 AM
11/05/23 10:16 AM
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markz528
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Got a picture of the damage?
A shorted field in the alternator for sure will cause the current to go high on that wire. The wire could be the weak link.
Last edited by markz528; 11/05/23 10:22 AM.
67 Coronet 500 9.610 @ 139.20 mph 67 Coronet 500 (street car) 14.82 @ 94 mph 69 GTX (clone) - build in progress......
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Re: 69 GTX Green Alt-Reg Wire Burnt Up
[Re: dragon slayer]
#3188881
11/05/23 11:27 AM
11/05/23 11:27 AM
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Sniper
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With Ohm meter you can check the alternator field terminal and see if you have 0 ohm short, or read some ohms. The rotor winding is the resistance in the field circuit. I am not sure how a ground in the regulator would damage the green wire as it would not force a high current on green wire. It would be 0 volts and low no output on alternator. To melt the green field wire it had to carry full voltage to ground to generate the current flow to melt insulation. Either rotor is shorted, the terminal insulator is broken/ground out, or the green wire had damage insulation that shorted to ground, but you said it was a tape wrapped wire, so probably not the issue. The old style mechanical regulator is either on or off, iow full voltage or no voltage. A shorted green wire could very well burn up but as I stated those old style mechanical regulators usually have an internal fusible link that goes before that happens. However, there is no path to ground for the green wire inside the regulator, at least not normally, that would have caused the meltdown had that wire been back fed from the alternator. Some measurements with an ohmmeter are needed here,
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Re: 69 GTX Green Alt-Reg Wire Burnt Up
[Re: markz528]
#3188996
11/05/23 08:13 PM
11/05/23 08:13 PM
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Dads426
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The owner pulled the alternator and the field terminal is grounded, which likely caused the high current flow through the wire. Haven’t heard back as to why it’s grounded. Will investigate further. Thanks for the tips.
2012 422 Allstars NSS Champion 2013 422 Allstars NSS Champion 2014 422 Allstars NSS Champion
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Re: 69 GTX Green Alt-Reg Wire Burnt Up
[Re: Sniper]
#3189013
11/05/23 09:34 PM
11/05/23 09:34 PM
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dragon slayer
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Why would the field terminal be grounded? The brush holder is most likely the culprit, assuming he didn't measure the one that is supposed to be grounded.
This is 69 car. So one brush is grounded. The rotor grounds out, the field terminal (on alternator) grounds out. Of course the insulator could be damaged and the terminal is touching case of alternator again grounding out. Easy to check once alternator is off the car.
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