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69 GTX Green Alt-Reg Wire Burnt Up #3188795 11/04/23 08:20 PM 11/04/23 08:20 PM
Joined: May 2007 Posts: 1,443 Maryland D Dads426 OP pro stock
Dads426 OP pro stock D Joined: May 2007 Posts: 1,443 Maryland	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! 2012 422 Allstars NSS Champion 2013 422 Allstars NSS Champion 2014 422 Allstars NSS Champion

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: Dads426] #3188801 11/04/23 08:48 PM 11/04/23 08:48 PM
Joined: May 2019 Posts: 6,241 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,241 nowhere	In that setup the regulator controls the 12v feed to the field windings, the other side of the field is grounded. So unless some sort of short inside the alternator some how shorted the stator to the field I dunno. I guess a continuity check between the BAT and the FLD terminals would tell that tale. Usually, there is a fusible link internal to the regulator to prevent a short in the green wiring from doing this sort of thing, at least with the original style mechanical regulator, not sure about the electronic version of this regulator though. I'm thinking some sort of short in the wire, did it get pinched under the valve cover, DAMHIK, lol.

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: Sniper] #3188804 11/04/23 09:13 PM 11/04/23 09:13 PM
Joined: Jan 2003 Posts: 15,350 Omaha Ne T TJP I Live Here
TJP I Live Here T Joined: Jan 2003 Posts: 15,350 Omaha Ne	Originally Posted by Sniper In that setup the regulator controls the 12v feed to the field windings, the other side of the field is grounded. So unless some sort of short inside the alternator some how shorted the stator to the field I dunno. I guess a continuity check between the BAT and the FLD terminals would tell that tale. Usually, there is a fusible link internal to the regulator to prevent a short in the green wiring from doing this sort of thing, at least with the original style mechanical regulator, not sure about the electronic version of this regulator though. I'm thinking some sort of short in the wire, did it get pinched under the valve cover, DAMHIK, lol. check the harness between the Alt and regulator carefully. It's not a long run and easy to get to. Also had one where the field terminal shorted to the alternator case www.tandmautomotive-omaha.com

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: Sniper] #3188806 11/04/23 09:20 PM 11/04/23 09:20 PM
Joined: May 2007 Posts: 1,443 Maryland D Dads426 OP pro stock
Dads426 OP pro stock D Joined: May 2007 Posts: 1,443 Maryland	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

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: Dads426] #3188810 11/04/23 09:56 PM 11/04/23 09:56 PM
Joined: Jan 2003 Posts: 21,507 N.E. OHIO, USA A12 Too Many Posts
A12 Too Many Posts Joined: Jan 2003 Posts: 21,507 N.E. OHIO, USA	Wonder what would happen if you just temporarily made a single wire independent of the wiring harness from the alternator to the regulator and checked the voltage on it? But it would seem to me that the regulator is shorted internally?

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: A12] #3188813 11/04/23 09:59 PM 11/04/23 09:59 PM
Joined: Jan 2003 Posts: 21,507 N.E. OHIO, USA A12 Too Many Posts
A12 Too Many Posts Joined: Jan 2003 Posts: 21,507 N.E. OHIO, USA	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?

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: A12] #3188819 11/04/23 10:39 PM 11/04/23 10:39 PM
Joined: May 2007 Posts: 1,443 Maryland D Dads426 OP pro stock
Dads426 OP pro stock D Joined: May 2007 Posts: 1,443 Maryland	Originally Posted by A12 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

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: Dads426] #3188855 11/05/23 09:26 AM 11/05/23 09:26 AM
Joined: Jun 2014 Posts: 1,322 VA D dragon slayer pro stock
dragon slayer pro stock D Joined: Jun 2014 Posts: 1,322 VA	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.

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
Joined: Jan 2003 Posts: 4,270 Morrow, OH markz528 master
markz528 master Joined: Jan 2003 Posts: 4,270 Morrow, OH	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......

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
Joined: May 2019 Posts: 6,241 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,241 nowhere	Originally Posted by dragon slayer 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,

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: dragon slayer] #3188975 11/05/23 07:02 PM 11/05/23 07:02 PM
Joined: Jan 2003 Posts: 15,350 Omaha Ne T TJP I Live Here
TJP I Live Here T Joined: Jan 2003 Posts: 15,350 Omaha Ne	Originally Posted by dragon slayer 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. And will add: that wire is wrapped in the harness that carries other wires. If it was hot enough to melt the insulation on the one wire, it is very likely the others may have been compromised. You should unwrap the harness between the regulator and alternator and inspect ALL the wires. Cheap insurance www.tandmautomotive-omaha.com

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: markz528] #3188996 11/05/23 08:13 PM 11/05/23 08:13 PM
Joined: May 2007 Posts: 1,443 Maryland D Dads426 OP pro stock
Dads426 OP pro stock D Joined: May 2007 Posts: 1,443 Maryland	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

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: Dads426] #3189000 11/05/23 08:27 PM 11/05/23 08:27 PM
Joined: May 2019 Posts: 6,241 nowhere S Sniper master
Sniper master S Joined: May 2019 Posts: 6,241 nowhere	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.

Re: 69 GTX Green Alt-Reg Wire Burnt Up [Re: Sniper] #3189013 11/05/23 09:34 PM 11/05/23 09:34 PM
Joined: Jun 2014 Posts: 1,322 VA D dragon slayer pro stock
dragon slayer pro stock D Joined: Jun 2014 Posts: 1,322 VA	Originally Posted by Sniper 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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