2 wires for alternator but three connectors, which two?

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Glad to help. I have been where you are with my own A-body and finally got I all worked out. Least I can do for all the help this place has been to me. So cool how everyone wants to help. I don't know it all but what I do know is all yours. And what I don't know I'll just ask someone around here. :)
 
Like a bad cold I'm back . . .

So adding to the diagnostics. I checked the battery with a volt meter after putting it on the charger and was getting about 12.6 volts. Started car and was expecting the battery to read around 14 but it never moves.

Checked my wiring to the alternator and all looks good. I am beginning to think I got a bad alternator (luckily it has a NAPA guarantee) but I did want to rule out the voltage regulator. I read that I can jump the ignition and field wire at the VR to bypass it and see if I get 14 at the battery, is that safe?

Thank you.
 
Jayman62 said:
Like a bad cold I'm back . . .

So adding to the diagnostics. I checked the battery with a volt meter after putting it on the charger and was getting about 12.6 volts. Started car and was expecting the battery to read around 14 but it never moves.

Checked my wiring to the alternator and all looks good. I am beginning to think I got a bad alternator (luckily it has a NAPA guarantee) but I did want to rule out the voltage regulator. I read that I can jump the ignition and field wire at the VR to bypass it and see if I get 14 at the battery, is that safe?

Thank you.
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I can't attest to bypassing the VR to test the alternator. I'll leave that up to someone else to chime in if they have. Few other things come to mind:
1) Is the alternator grounded sufficiently when installed? Check continuity from alternator casing to (-) side of battery. Should read zero or very close to it when measuring resistance.
2) Couldn't hurt to replace the VR. They aren't that expensive. If it winds up not being the issue you'll have a spare.
3) Have NAPA test the alternator for you. In all the fiddling around so far something may have gotten compromised with it.
 
You can't measure the field resistance with your ohmmeter on the 2000 kohm range you stated (2 megohm max). Doesn't your multimeter have a 200 ohm range setting? The field resistance is something like 10 to 20 ohms, to draw maybe 0.5 to 1 amp (kind of guessing). To test your alternator without risking damage to the Vreg, unplug the single Vreg wire (green) and externally apply 12 VDC to that spade terminal using a thin alligator clip jumper. You can add a fuse in series if really worried or just let the jumper insulation melt if too much. That should "full field" the alternator, and you can read the output on the dash ammeter. If working, you should measure ~14.3 VDC at the cigarette lighter with alternator running and ~12.6 VDC with engine off and battery fully charged.
 
BillGrissom said:
You can't measure the field resistance with your ohmmeter on the 2000 kohm range you stated (2 megohm max). Doesn't your multimeter have a 200 ohm range setting?
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@BillGrissom, you are correct. Measuring a particular resistance value such as the field circuit resistance, a specific range needs to be selected on the meter as you indicated (unless the meter is auto-ranging of course). However in the case of the OP here he was at no time measuring resistance of the field circuit itself. He was measuring the terminals on the alternator in relation to ground only. It was only to determine whether the alternator was rebuilt as a '70 & newer alternator replacement or a '69 & older alternator replacement. The '69 & older alternator casings are becoming more scarce so many rebuilds for them are on a '70 and newer casing, hence one of the terminals will be clipped and grounded.
 

If you are running the older pre-70 VR with one field wire, one brush grounded, FEED 12V to the alternator field terminal after disconnecting the VR. You can also disconnect the VR and jumper the two VR wires together--this will feed from ignition switch to (green) alternator field. IF THAT wiring is ok, the alternator should charge full output when RPM is up "a bit." Monitor battery voltage, and do not allow battery to rise above 16V

If you are running the 70/ later VR "isolated field" you will have a wire to one field from the key, and the green wire to the VR. To "full field" that one, ground either field, and feed 12V to the other terminal. Or, verify the feed to the one field from the key is getting power, then ground the line which went to the VR.

The field is simply an electromagnet........feed it 12V and rotate the alternator, and it makes power. Reduce the field current, and it makes less power. Reduce RPM, and it makes less power
 
67Dart273 said:
If you are running the older pre-70 VR with one field wire, one brush grounded, FEED 12V to the alternator field terminal after disconnecting the VR. You can also disconnect the VR and jumper the two VR wires together--this will feed from ignition switch to (green) alternator field. IF THAT wiring is ok, the alternator should charge full output when RPM is up "a bit." Monitor battery voltage, and do not allow battery to rise above 16V

As @67Dart273 stated, "MONITOR BATTERY VOLTAGE" and don't let it rise too high. Bad things can happen quickly. I learned this the hard way myself one time.
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Figured I report back in case another person follows me down this rabbit hole. My issue turned out to be a bad alternator, it was swapped out by NAPA at no charge (no pun intended). Hooked it up and charging as expected. Thank you for all the guidance and knowledge I gained. I also wound up replacing the voltage regulator just so all the components of the charging system were new.

Jay
 
Jayman62 said:
Figured I report back in case another person follows me down this rabbit hole. My issue turned out to be a bad alternator, it was swapped out by NAPA at no charge (no pun intended). Hooked it up and charging as expected. Thank you for all the guidance and knowledge I gained. I also wound up replacing the voltage regulator just so all the components of the charging system were new.

Jay
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Yeah man, good deal. Thanks for keeping us in the loop til the end. Until the next big one, lol. - Nick
 
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