What are the values?
We're both wires removed at the same time when tested?
We're both wires removed at the same time when tested?
Diagnosing high voltage
- Thread starter hotrod swinger
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hotrod swinger
Well-Known Member
Both were disconnected when tested. I didn’t think the values were relevant so I didn’t make a note, I thought we were just looking at open or closed. If the values mean something I will go test again. I recall it seemed like both were pretty low resistance.
If you know the resistance of each terminal you might find a short on one or the other. The lowest numerical resistance would be closest to the short to ground.
Might just need to turn the terminal a tad.
But the low numerical resistance on either terminal would suggest a fault with the alternator.
Might just need to turn the terminal a tad.
But the low numerical resistance on either terminal would suggest a fault with the alternator.
hotrod swinger
Well-Known Member
Have I narrowed it down to a fault with the alternator?
I think so.
Pull it and have the local parts store test it.
Pull it and have the local parts store test it.
hotrod swinger
Well-Known Member
Found this on b-bodies:
step 1. unhook both small spade terminals to alternator and start car, it should not charge at all. if it does its a bad alternator.
step 2 hook up the small 12v wire to the bat spade terminal on alternator but leave the green wire off the field terminal, if it charges at all its a bad alternator.
step3 hook up all 3 wires on alternator, unplug triangle plug on voltage regulator, if it charges than the green wire from alternator to regulator is shorted to ground.
step 1. unhook both small spade terminals to alternator and start car, it should not charge at all. if it does its a bad alternator.
step 2 hook up the small 12v wire to the bat spade terminal on alternator but leave the green wire off the field terminal, if it charges at all its a bad alternator.
step3 hook up all 3 wires on alternator, unplug triangle plug on voltage regulator, if it charges than the green wire from alternator to regulator is shorted to ground.
67Dart273
Well-Known Member
Here's the thing. "Screwing around" can change the problem. EITHER brush can be grounded, you have a 50-50 chance. If the one connected to the blue is shorted, OR YOU reverse the field wires, you WILL BURN DOWN THE ignition harness
As others pointed out, test either or both brush holders with a continuity lamp or meter to ground. Both should be open. The problem can be right in the rotor (burned windings / shorted to ground) or in the brush holders, either one of them
hotrod swinger
Well-Known Member
I posted earlier that both alternator terminals are shorted to ground.
hotrod swinger
Well-Known Member
With my voltage regulator disconnected, my voltmeter shows severe overcharging consistent with increased RPM.
Of course if does - until it burns something out.
Identifying Chrysler Alternators (1960-1976)
Post 5 explains why but requires reading the first post about anatomy.
Identifying Chrysler Alternators (1960-1976)
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Then what Del wrote in post #32 above should make sense.
If not, ask questions.
The answers are all there.
Its now mostly a matter of how you learn best.
I'll say this, and this goes back Before Internet.
For a long time I looked for procedural answers. Step 1 do this. Step 2, do that. Some of the later service manuals have these. AMC called them DARS charts. These are not nearly as helpful as they seem. Troubleshooting requires understanding what the parts do and how they work together. Then the procedures suggested will makes sense, and even if they don't apply can sometimes be useful as an example of how to approach the problem.
For me, understanding what the parts do and how they work together required both the explanation and holding the parts in my hand. Everyone learns differently. I could do the math for a differential in school but really didn't understand in the same way until I saw one - and I don't mean just a picture. That's just me. So you have the parts in hand, I'm hoping when you read what they do and how they work together it will start to click.
If not, ask questions.
The answers are all there.
Its now mostly a matter of how you learn best.
I'll say this, and this goes back Before Internet.
For a long time I looked for procedural answers. Step 1 do this. Step 2, do that. Some of the later service manuals have these. AMC called them DARS charts. These are not nearly as helpful as they seem. Troubleshooting requires understanding what the parts do and how they work together. Then the procedures suggested will makes sense, and even if they don't apply can sometimes be useful as an example of how to approach the problem.
For me, understanding what the parts do and how they work together required both the explanation and holding the parts in my hand. Everyone learns differently. I could do the math for a differential in school but really didn't understand in the same way until I saw one - and I don't mean just a picture. That's just me. So you have the parts in hand, I'm hoping when you read what they do and how they work together it will start to click.
Not sure why you are still trying to diagnose the problem.
You stated that there is low numerical resistance to ground on both field wires with both field terminals removed at the same time.
That says that one of the terminals OR an I thermal shirt exists
The fact that you can remove the VR connector and it is still charging Proves that as well.
PULL THE ALTERNATOR, TAKE IT TO THE PARTS STORE, HAVE THEM TEST IT, THEN GO HOME WITH A NEW ONE AND INSTALL IT.
AAAAARRRRRRGGGGGG!
67Dart273
Well-Known Member
What we are trying to say:
Seems like you have the trouble localized. Time to yank the alternator
Look at the brush terminals. Take them apart. Look for broken/ missing insulators/ hardware. If that does not result in an answer, then remove the brushes and holders completely, and with one probe on the case, probe either available slip ring directly. If you get ANY continuity to the case the rotor is grounded. Otherwise, look to fix the broken brush assembly, or replace the alternator.
I'm with Mattox. I rarely try to memorize "step one, two three" troubleshoot procedures, except "generally." Start somewhere and go left to right, up or down. Try to keep in mind "the path." Where does it start, where does it end, what is the desired end for the effect and so on. Don't be afraid to get frustrated, drop that line of thought, and "rethink."
Seems like you have the trouble localized. Time to yank the alternator
Look at the brush terminals. Take them apart. Look for broken/ missing insulators/ hardware. If that does not result in an answer, then remove the brushes and holders completely, and with one probe on the case, probe either available slip ring directly. If you get ANY continuity to the case the rotor is grounded. Otherwise, look to fix the broken brush assembly, or replace the alternator.
I'm with Mattox. I rarely try to memorize "step one, two three" troubleshoot procedures, except "generally." Start somewhere and go left to right, up or down. Try to keep in mind "the path." Where does it start, where does it end, what is the desired end for the effect and so on. Don't be afraid to get frustrated, drop that line of thought, and "rethink."
hotrod swinger
Well-Known Member
I will pull the alternator and examine the brushes.
In the meantime, here’s a question for you:
I have installed an 8 gauge jumper wire from alternator to battery with a 12 gauge fusible link.
I have also installed a relay in my ignition circuit under the hood. Am I correct that the fuse in that circuit should protect against burning up the ignition harness?
The reason I ask is that I was thinking I would install a fusible link in the black alternator wire as part of my reinstall, but if the fuse in the ignition circuit protects me I won’t bother.
In the meantime, here’s a question for you:
I have installed an 8 gauge jumper wire from alternator to battery with a 12 gauge fusible link.
I have also installed a relay in my ignition circuit under the hood. Am I correct that the fuse in that circuit should protect against burning up the ignition harness?
The reason I ask is that I was thinking I would install a fusible link in the black alternator wire as part of my reinstall, but if the fuse in the ignition circuit protects me I won’t bother.
hotrod swinger
Well-Known Member
I replaced the alternator. I am going to keep the old one and rebuild it. Should learn to do that anyway, seems silly to buy a whole new alternator when it can possibly be fixed with a cheap part.
I am really interested to know whether or not my ignition circuit relay and fuse will protect me against a short inside the alternator.
I was lucky it was the green connection and I caught it in time with my voltmeter.
If there is a short on the blue connection my fuse should blow, which I would think would prevent the alternator from generating any power, am I wrong?
I am really interested to know whether or not my ignition circuit relay and fuse will protect me against a short inside the alternator.
I was lucky it was the green connection and I caught it in time with my voltmeter.
If there is a short on the blue connection my fuse should blow, which I would think would prevent the alternator from generating any power, am I wrong?
hotrod swinger
Well-Known Member
Regretfully the new alternator didn’t work. Took the car for a drive, back to having severe high voltage.
The new alternator passes all resistance checks.
Now what? I’m lost.
The new alternator passes all resistance checks.
Now what? I’m lost.
On the new alternator, do the resistance test as outlined in post 24, and report back the values from your meter.
hotrod swinger
Well-Known Member
New alternator:
blue to ground open
green to ground open
Between the two is 4
Also confirmed green wire is not shorted to ground
blue to ground open
green to ground open
Between the two is 4
Also confirmed green wire is not shorted to ground
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67Dart273
Well-Known Member
"Follow the path." And start over as if it is a new problem. Functional path is key--through harness---to junction in engine bay---to VR "blue" (ign) terminal. Through guts of VR to ground
Second path is key--harness--blue--to VR field--through field--out on green--back to VR and to ground through VR
1...Disconnect the green from alternator, make sure it does NOT charge. If that is true, take a alligator lead and ground the field that was connected to the green. Make sure it charges and it will OVER charge. Reconnect green
2....Disconnect VR connector. Run and make sure it does NOT charge. If not, make sure VR is grounded. REALLY grounded
RE check voltage as close to VR as you can get. IT MIGHT BE time to find a pin/ needle to puncture into the VR blue wire terminal at the VR with it all connected up. RE-measure V drop between VR blue terminal and battery plus. If this is OK,
Check as well as you can that VR connector is in good condition. If so, replace VR
If there is ANY doubt as to condition of VR connector, last I knew NAPA had these
It should also be possible to "jerry rig" VR to sorta test connector condition. Connect an alligator lead to VR blue terminal at VR ("top" terminal) Jumper this over to a battery source
Clip second alligator lead to "side" terminal of VR (where green connects) and run that over and connect to the terminal on the alternator where the "green" normally sits. This should eliminate any harness drop or poor connections for testing and prove, at least, that the VR works properly. Again, make CERTAIN VR is GROUNDED
Second path is key--harness--blue--to VR field--through field--out on green--back to VR and to ground through VR
1...Disconnect the green from alternator, make sure it does NOT charge. If that is true, take a alligator lead and ground the field that was connected to the green. Make sure it charges and it will OVER charge. Reconnect green
2....Disconnect VR connector. Run and make sure it does NOT charge. If not, make sure VR is grounded. REALLY grounded
RE check voltage as close to VR as you can get. IT MIGHT BE time to find a pin/ needle to puncture into the VR blue wire terminal at the VR with it all connected up. RE-measure V drop between VR blue terminal and battery plus. If this is OK,
Check as well as you can that VR connector is in good condition. If so, replace VR
If there is ANY doubt as to condition of VR connector, last I knew NAPA had these
It should also be possible to "jerry rig" VR to sorta test connector condition. Connect an alligator lead to VR blue terminal at VR ("top" terminal) Jumper this over to a battery source
Clip second alligator lead to "side" terminal of VR (where green connects) and run that over and connect to the terminal on the alternator where the "green" normally sits. This should eliminate any harness drop or poor connections for testing and prove, at least, that the VR works properly. Again, make CERTAIN VR is GROUNDED
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hotrod swinger
Well-Known Member
Ok, starting over.
Voltmeter is pegged, 17V.
Again, voltmeter pegged at 17V with VR disconnected.
Voltage drop at VR with key in run is 0.20V.
VR is grounded and connector looks good.
Voltmeter is pegged, 17V.
Again, voltmeter pegged at 17V with VR disconnected.
Voltage drop at VR with key in run is 0.20V.
VR is grounded and connector looks good.
hotrod swinger
Well-Known Member
Should I get the battery tested?
hotrod swinger
Well-Known Member
I swapped in a spare VR, didn’t make a difference.
I’m absolutely sure the VR is grounded. I have it mounted with three bolts, star washers, paint removed, tested with the voltmeter.
I guess it’s possible my spare VR is also malfunctioning.
Any more tests I can do?
hotrod swinger
Well-Known Member
When I unplug the VR and run the car I still have a severe overcharge.
67Dart273
Well-Known Member
Then it HAS to be that the green wire is shorted (to ground) OR there is a problem in the alternator.
Eliminating the VR, the alternator field is simply an electromagnet. From key--through harness--to alternator field on the blue wire--through the field--and the VR controls the "ground" or if you remove it and YOU short the field to ground (or something else does) then you have output. If you remove the ground and the field/ brushes are OK, it can not charge.
Eliminating the VR, the alternator field is simply an electromagnet. From key--through harness--to alternator field on the blue wire--through the field--and the VR controls the "ground" or if you remove it and YOU short the field to ground (or something else does) then you have output. If you remove the ground and the field/ brushes are OK, it can not charge.
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