71 dart, o.e engine harness and connections. Checked all connections and batt voltage, all grounds look good. Field wires Not reversed. Double checked ign switch and tried a new one to test. Ok. Two regulators one new one used both act the same. Battery at 12.9 no load. Shoots to 18 volts at about 2k rpm. Stays high with any kind of rpm. New problem all components were working together prior to this….?? Any ideas..Thanks in advance….Swingn..
Alternator Full fielding..??
- Thread starter Swingn’71
- Start date
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Assuming you have a a isolated field alternator (typically square back in design and 2 field wires)
One of your field wires is 12v from ignition switch and the other is a variable ground from the voltage regulator.
If the wire from the voltage regulator gets grounded you will have the situation you describe.
A quick check is to see if there is 12v to ground to one field wire at the alternator while it is running and the other field wire to ground should be other than 0 volts like 5 to 10. If it is 0 volts to ground then disconnect it from the VR and test again at the alternator. If it is still 0v then that wire is shorted to ground somewhere along it's path.
One of your field wires is 12v from ignition switch and the other is a variable ground from the voltage regulator.
If the wire from the voltage regulator gets grounded you will have the situation you describe.
A quick check is to see if there is 12v to ground to one field wire at the alternator while it is running and the other field wire to ground should be other than 0 volts like 5 to 10. If it is 0 volts to ground then disconnect it from the VR and test again at the alternator. If it is still 0v then that wire is shorted to ground somewhere along it's path.
Make sure the regulator is properly grounded to the firewall.
Ummmm.....what? I assume you mean firewall? lol
I know I caint stand it. Same with Ebay's auto suggestions. That REALLY ticks me off. lolDamn spell check!
Yes, two field alt, Thanks, will check this afternoon. Another reply mentioned a internally shorted alt..?? Common..?? Can’t say I have had it happen. Thanks again. Will check and report fidings…..Swingn’
Yes, 10-4 good ground to wall short jumper to master cyl stud also….Thanks for the reply…Swingn’
10-4 another possibility…Thanks.
I don't think so, but easy to check. Pull both field wires off the alternator and check for continuity to ground at each field terminal on the alternator.
There is no reverse. Doesn't matter which brush is on the supply side and which is going back to the regulator (green wire).
Key off. Take a multimeter set on resistance or continuity. Put one probe on the alternator housing and backprobe each brush terminal.
If they connect with ground, then its in the alternator or the wiring. Disconnect each field wire from the brush terminals. Check each until you find the one that's grounding.
If is not grounding with key off, then its probably a faulty regulator.
The regulator works by completing the circuit to ground.
It'll also full field if you lose the blue power wire connection at the regulator! Mine broke off inside the plug..
1WildRT
Well-Known Member
Or just unplug the green wire going to the alternator... Leave the blue wire connected... Does it stop charging? If it does the alternator isn't the problem...
Next plug the green wire into the alternator & disconnect the plug on the regulator... Does it charge now? Then the green wire between the alternator & regulator is shorted to ground... If not the problem is further up the line...
As mentioned the regulator meeds a good ground... But it also needs to see full charging voltage on the blue wire, thats the voltage regulators reference voltage... If it only sees 10v on the blue wire it's gonna ground the green wire causing the alternator to charge...
That's a good point.
The blue wire connection on the regulator is the sensing connection.
If the regulator senses low voltage, or in that case, no voltage, it connects the green wire directly to ground and keeps it there in an attempt to increase the voltage.
Good way to solve it when there's no meter or lamp handy!
Wow…10-4..Thanks for all the help…!!! To everyone..!! Will report back as soon as I know…Swingn’
67Dart273
Well-Known Member
THIS AND there are MANY cases where BROKEN or MISSING parts in the brush holders cause one brush to be GROUNDED. You have a 50-50 chance
If the brush connected to the green wire grounds, it will "full field"
If the brush connected to the blue 12V wire grounds IT WILL DAMAGE THE HARNESS
Thanks for the explanation..!! Will check later today, so wiring aside checking the “fields” first (at the alt) to make certain they are not going to ground..?? Swingn’
67Dart273
Well-Known Member
That's right. Use ohmeter, check "field to field" should show quite low resistance
Check both terminals to case, both should show infinity
There are rare cases where a rotor can short internally to the "shaft" and this can cause this conditon, but rare. By far the more common cause is brush / brush holder problems........mistakes in hardware by rebuilders, MODIFIED (round back modified to isolated field) by rebuilders, or mistakes in owner assembly, broken or missing brush holder parts
Check both terminals to case, both should show infinity
There are rare cases where a rotor can short internally to the "shaft" and this can cause this conditon, but rare. By far the more common cause is brush / brush holder problems........mistakes in hardware by rebuilders, MODIFIED (round back modified to isolated field) by rebuilders, or mistakes in owner assembly, broken or missing brush holder parts
1WildRT
Well-Known Member
70-71 round back are originally isolated field... Owning & restoring may 70 vintage vehicles I've had more trouble with supposedly isolated field alternators that are built wrong, have the two connectors but internally grounded.. And yeah, usually the problem is in how the brush holders are assembled.... And why I prefer to build my own rather than have a rebuilder do it....
30 years ago rebuilders knew these old cars... Not so much these days..
67Dart273
Well-Known Member
You have to be careful. Here is an oddball roundback. This one has a GROUNDED brush installed at 9 o'clock, an isolated brush at 12 o'clock, and a blank for an isolated brush at 3 o'clock. I assume this is an aftermarket piece. The danger is if you were to have all three installed, and they try to use it "isolated." (70/ later)
This is the "pinnacle" of a junk rebuilder who modified a grounded brush roundback to take a second isolated brush. This one also has a grounded brush installed. All they have done here, is drilled a hole in an older case The normal isolated brush is at 3 o'clock, the installed grounded brush is at 6 o'clock, and the unused drilled hole/ modified isolated brush position is at 12 o'clock
This is a 70/ later isolated field unit before squarebacks came out
This is the "pinnacle" of a junk rebuilder who modified a grounded brush roundback to take a second isolated brush. This one also has a grounded brush installed. All they have done here, is drilled a hole in an older case The normal isolated brush is at 3 o'clock, the installed grounded brush is at 6 o'clock, and the unused drilled hole/ modified isolated brush position is at 12 o'clock
This is a 70/ later isolated field unit before squarebacks came out
A quick update..Checked both fields to alt case..ok not going to ground. Green wire disconnected no charge. Seems to be some voltage drop at blue wire at regulator. Any real formula to determine how much a 1/2 or full volt would “up” the charge rate..?? Thanks Swingn’
67Dart273
Well-Known Member
Whatever the drop is you measure will be added to the VR setpoint. So "if" the VR is not faulty it will want to charge about 14 when warmed up. If you measure 1.5V in the drop test, it will "run" the battery at 14+ 1.5 =15.5 V
Also notice the chart and temp. The VR is temp sensitive, so when evaluating system voltage get the engine warmed up to warm the engine bay and battery and VR and get the battery "up and normalized."
Also notice the chart and temp. The VR is temp sensitive, so when evaluating system voltage get the engine warmed up to warm the engine bay and battery and VR and get the battery "up and normalized."
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