Alternator and electrical basics with a multimeter

[Craven2112]

Hello all and thanks for welcoming me. On my recently acquired 65 dodge dart I am not making charging voltage. I’ve swapped out the voltage regulator and an alternator from O’Reillys. I know that alternators remanufactured in China showing up DOA out of the box is not uncommon With this new remanufactured alternator if I put my multimeter on the battery terminal of the alternator with the other lead to battery ground I don’t get more than 12.6 V. Same result with the negative lead on the multimeter touching the frame of the car. I can’t think of anything as far as a ground problem, or any other explanation other than bad alternator, is there anything else that could cause a lack of charging voltage? The alternator gauge in the car is functioning, and I have never seen it go into the positive only into the negative or discharge.

Having said all that, I am smitten and 100% in love with this car and I’m enjoying the opportunity to work on it and work on it with my kids. My 11 year old boy swapped out the voltage regulator himself, and my 13-year-old stepdaughter is absolutely in love with the car, and has taken it upon herself to begin learning all about engines and can identify all the major components and understands the basic principles of the internal combustion engine. Proud dad and stepdad here. Thank you.

 

[slickchick]

Check all of your grounds,body ground,voltage regulator ground to body. Start there

 

[RedFish]

OK, You first need a basic history lesson on Chryslers charging system. In the beginning they created what is known as a closed field alternator and the appropriate closed field regulator. That (mechanical) regulator had simply a blue wire at top receiving 12 volts at ignition switch on, and a green wire that went to the alternators field or one contact brush on its armature. the other side of the field was chassis grounded like nearly everything else that operated on 12 volts. Some still refer to this practice as "raceway" grounding. No ground wire is required because the body is metal. Thus the vehicle itself serves as a ground wire. Those alternators were called round back by the peeople that dealt with them simply because they had a roundish backside.
Now lets fast forward to the square back alternator which was a different electrical design know as isolated field alternator. This alternator used a different solid state regulator. It had the same green wire going from regulator to on contact brush on back of the alternator but also had a blue wire (same circuit as blue wire on either regulator type mention before). This blue wire energized the field so the green wire only senses and feeds back to the regulator where it is grounded. This alternator was and still is referred to as square back. The novice would call it a dual field alternator simply due to the 2 wires on field contacts/brushes.
There are reasons why the round back alternators are no longer reproduced. One reason, their output was only 36 to 42 volts. That is very minimal power by todays standards.
Cut to the chase, I'll sit here many miles away and guess you do have a square back alternator, be it brand new or reman'd. The parts clerk was correct when stating this alternator would work in your application. He likely didn't explain what the difference is and how to go about making it work. I will....
Assuming you have the correct regulator for closed field type unit, You would simply attach the green wire to one of the contact/brush terminals and addon a jumper wire routed from the other brush terminal to chassis ground. Now the isolated field "square back" alternator operates as a closed field alternator. It can produce 60 amps or more but not to worry. A proper functioning voltage regulator will not allow more system current than called for by the system.

 

[67Dart273]

Some simple tests:

I tend to think of these systems as, the output circuit, which comes off the big stud, the big black wire, that is the output, goes through the firewall connector, through the ammeter, branches off to feed power into the car, back out through the firewall connector on big RED, through fuse link,and to battery

Next the field / control circuit. The dark blue "run" wire which feeds ignition system branches off to feed the VR IGN (ignition) terminal, and the VR MUST be grounded. Through the VR, and out on green to the field terminal on the alternator, through the field, which is simply an electromagnet, and to ground through the second brush in the alternator

Possible problems are, a break in the output circuit, preventing alternator output from reaching the battery

Breaks in wiring / terminals

A break in the field wiring, preventing igntiion "run" voltage from reaching the VR, or actually in the green wire, which has happened (guy got the green wire pinched under a rocker cover!!)

Bad VR

Bad alterator

SO.............................Remove the green wire from the alternator field, and rig a jumper wire from the alternator field terminal to the battery. In quiet, subdued lighting, you may hear and or see a very small spark if you connect/ disconnect that wire.

Now start and run the engine, slowly bring up RPM, and see if the ammeter charges. Monitor battery voltage and see if it comes up with a multimeter. Try not to let it go above 16V

If this does not charge, check the output circuit. With the same field jumper in place, transfer your meter to the alternator output stud and run engine again, see if that reading comes up. If not, if it remains below 13V the alternator is not charging. Either repair or replace it.

If the alternator DOES charge with this jumper, not check your VR wiring.

Connect everything up normally again. This time, disconnect the two VR wires and rig a way to jumper between them, AKA connect the blue and green VR wires together. Again, start, run engine, see if it charges. If so, the VR wiring is OK, replace the VR

If you do not have one, run over to MyMopar.com and download a factory service manual, as well as one of the aftermarket wiring diagrams, which are now inexplicably a PITA because they are zipped. Those diagrams are NOT as complete as the factory ones, but can be somewhat easier to follow I use both

Once you run these tests, post back and we will go from there. Once you get it working you MAY NOT be done, as the ammeter circuit may be damage, and also voltage drop in old wiring can cause OVER charging.

 

[67Dart273]

This is a simplified circuit of the pre 70 alternator / regulator

At the top, labeled "ignition" is coming from the ignition switch dark blue "run" wire which also feeds the ignition system. Through the VR WHICH must be grounded, out on the field FLD terminal, and to the only terminal on the alternator through the green wire. The second field terminal shown to ground normally does not actually appear external to the alternator. IF YOU buy a more modern replacement, THAT SECOND FIELD may need to be grounded externally. PHOTOS are the only way

The RED "batt" wire is oversimplified. It does NOT go direct to battery, but rather through the ammeter circuit as I mentioned earlier

 

[Dana67Dart]

Watch these videos

69 and older single field wire alternator and VR.



70 and newer isolated (2 wire) field wire and VR.

 

[Craven2112]

Ya’ll are AWESOME. thank you for all the help. Getting antique plates now, will get back to work and report back! There is no ground from the alternator as described in that loop from the additional post so I’m gonna tackle that!

 

[MiradaMegaCab]

What’s the voltage from the large alternator stud to ground?

You might have a bad fusible link

 

[67Dart273]

What’s the voltage from the large alternator stud to ground?

You might have a bad fusible link

No. Bad fuse link will kill ALL power into the car, including headlights

 

[pt70]

Post #5 diagram is confusing. The field [-] is the brush and brushholder. It has a screw that holds in onto the alternator housing. This is your ground.

The field [+] is the other brush and brushholder. It is isolated from the alternator housing with special washers. Unplug the green wire from the alternator. Grab your test light [an incandescent bulb type with a 4' wire and an alligator clip] and push it into the green wire connector. Mount the alligator clip onto the alternator housing. Check for safety. Turn ign. key to on. The light should go on.

 

[Mattax]

I’ve swapped out the voltage regulator and an alternator from O’Reillys. I know that alternators remanufactured in China showing up DOA out of the box is not uncommon With this new remanufactured alternator if I put my multimeter on the battery terminal of the alternator with the other lead to battery ground I don’t get more than 12.6 V. Same result with the negative lead on the multimeter touching the frame of the car. I can’t think of anything as far as a ground problem, or any other explanation other than bad alternator, is there anything else that could cause a lack of charging voltage? The alternator gauge in the car is functioning, and I have never seen it go into the positive only into the negative or discharge.

1. Put the battery on a charger. Driving around on battery power is running it down. I know, that's obvious. Less commonly recognized is what will happen when the altenator is asked to recharge a battery that is very low. Supplied at 14 volts from the alternator, the battery recharging will draw a lot of current for a relately long period of time. The ammeter will show this, but there is not a lot that can be done about it. if you're ever stuck in this situation, kick the engine down to slow idle as soon as possible. The alternator will max out and help save the reduce eating the wiring and battery.

2. The ammeter always shows discharge because its in the battery feed/charge wire. Even though it says "alternator" on it, it does just what you obderved when the alternator is not working. Schematically the wiring for your '65 looks like this:

Notice where the ammeter is. When the alternator is powering the ignition, headlights, wipers, current will flow directly to those items. The only current that deflects the ammeter is coming from or going to the battery.

3. Photos and Illustrations of the Alternator parts and what they do are here: Identifying Chrysler Alternators (1960-1976)

Rebuilt alternators have a tendency to come with higher draw rotors (field) than original. This is true of both square back and round back. Revised squareback came that way originally. Avoid these if at all possible. Your car was not built to have that many additional amps going through the ignition run circuit. Also the regulators seem to have more difficulty controlling the field.

 

[67Dart273]

Post #5 diagram is confusing. The field [-] is the brush and brushholder. It has a screw that holds in onto the alternator housing. This is your ground.

The field [+] is the other brush and brushholder. It is isolated from the alternator housing with special washers. Unplug the green wire from the alternator. Grab your test light [an incandescent bulb type with a 4' wire and an alligator clip] and push it into the green wire connector. Mount the alligator clip onto the alternator housing. Check for safety. Turn ign. key to on. The light should go on.

I explained that, I thought.