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MarvinG · 09-08-2019, 10:55 AM

Last week, I took my rig in to fill with gas while gas prices were down. I noticed the battery was not charging well but enough to keep running throughout the day. Did some troubleshooting, battery is almost new, charged it, to make sure it had no shorted cells. Finally ordered a new alternator from Autozone. Installed it this morning. If anything it is worse with no output.

I have the same voltage at the alternator output that I have at the battery terminals measured with a digital multimeter. Also seems like the battery is more discharged then it should be after just sitting there (with the ground disconnected) for several days. My charged battery voltage was around 12.6 or 7 and now I am looking at 12.3 before starting the rig and 11.9 after starting.

I am doubtful a new alternator would exhibit the same failure symptoms. What should I be checking next? Am I not getting voltage to the field pin(s)? Any troubleshooting tips are appreciated!

1ciderdog · 09-08-2019, 11:43 AM

Is it possible the new alternator is defective? Is the new alternator putting out 13+ volts?

TeJay · 09-08-2019, 03:02 PM

MarvinG, follow what 1ciderdog said.

If you checked the alternator output before changing it and it was in the 11 V range then the alternator was not charging.

What is the alternators output now?? New does not always mean it works.

If it's not 12.6 or at least 1 V above the battery's static voltage it won't charge the battery. So then the NEW alternator is defective. It's an Auto Zone alternator. Usually the first two you get are defective.

A word to the wise should be sufficient. Don't try to save to much $$$$$ buying cheap. With something like an alternator or starter I'd either go back to the manufacturer dealer or to a NAPA store and buy their best. Most of the better ones will have a decent warranty as well.

After 35 years Teaching HS automotive and working on all kinds of vehicles I buy few parts from the lower end parts houses. Especially when it comes to things that have to work at least 98% of the time or I don't move. It's just not worth my time to install a less than quality part.

subford · 09-08-2019, 03:03 PM

Check the red and green striped wire from the cluster at the Generator (Alternator):

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twinboat · 09-08-2019, 03:20 PM

When I first read this post, and the OP said he had no voltage on the field wire, what first came to my mind was " Subford would send some troubleshooting advice ", and he did.

Just exchanging alternators over and over again, without troubleshooting the system, is just throwing parts at it, hoping it will fix itself.

To the OP, did you have the alternator you removed tested or just exchange it ?

sibe · 09-08-2019, 03:34 PM

regulater is seperate.. probably bad

twinboat · 09-08-2019, 05:32 PM

Quote:

Originally Posted by sibe

regulater is seperate.. probably bad

Seperate regulator In 1996 ?

aether_one · 09-08-2019, 05:36 PM

Quote:

Originally Posted by sibe

regulater is seperate.. probably bad

Quote:

Originally Posted by twinboat

Seperate regulator In 1996 ?

I guess the OP has a spare alternator now. As I recall no refunds on electrical components.

MarvinG · 09-08-2019, 06:26 PM

Correct, I may very possibly now have a spare alternator. I agree that low end house parts are not always best, however, I bought new rather than rebuilt and do have a lifetime warranty if I prove the new alternator is bad. However I’m doubtful at this point that it is bad. I also agree new does not mean it is good but I do have to make sure the new one is defective before I change it out again.

I haven’t said I don’t have voltage at the field, but that is the next thing I want to check so thank you for the wiring diagram. That will help me tremendously.

The original (rebuilt motorcraft which was on the rig when I bought it 3 years ago) had a slight output above battery voltage and that is why I double checked the battery to make sure it wasn’t so badly shorted the alternator couldn’t output enough voltage to overcome it. I’m still not sure the almost new battery is good but it should be good enough to allow the alternator to charge.

The new alternator has NO output above battery voltage. So unless someone has a better idea, I’ll make sure the field is getting voltage. This has internal (actually stuck on the side) regulator I think it is called the G3 alternator where you have a plug onto the regulator I believe and a jumper wire coming out of the plug to the field.

MarvinG · 09-08-2019, 06:53 PM

I’m measuring 1.96 volts on the red/green wire at the plug to the alternator with it plugged into the alternator. Essentially no voltage with it unplugged. With it unplugged the battery dash light does not light up. With it plugged in I am getting the dash battery light. Should I be getting full battery voltage? If so will I damage anything by jumping + voltage to that wire to see if I get full alternator output?

subford · 09-09-2019, 06:12 AM

The “I” Circuit (Light Green wire with a Red stripe, circuit #904).

The I circuit, or ignition switch circuit is used to turn on the following:
* voltage regulator (VR) (10316)
* ignition switch (11572) which is powered up with the ignition switch lock cylinder (11582) in the RUN position
* the indicator circuit if there is a fault in the charging system operation or associated wiring circuits

With wire #904 unplugged at the alternator, key in run position you should have near battery voltage on the #904 wire.
The alternator should not be hurt by just jumping the "I" point on the alternator for a very short time while the volt meter is on the alternator out put connection (BK/O wire) for a test with the #904 wire disconnected from the alternator. Do not put power to the #904 wire while it is removed from the alternator as the #904 wire may be shorted to ground and if so sparks will fly.

Note the #4 wire is also in the same connector as the #904 wire and if the #4 wire is not connected the alternator it will not charge. So #904 wire should be removed from the connector for the test.

subford · 09-09-2019, 09:29 AM

Edit to the above.
You will not be able to separate the #4 "S" wire from the #904 wire at the Regulator plug connector. REF the image below.

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MarvinG · 09-10-2019, 05:04 AM

Right. I’m going to cut the wire coming into the plug and test. When this is completed I’ll butt splice it back and seal and tape it. I should have a few moments this morning to test. If voltage coming in is the problem, I may simply run a new wire if I can’t easily trace it through multiple connections.

subford · 09-10-2019, 07:38 AM

Do not cut the wire.
There is a single wire connector that you can disconnect.
It is C147 in the diagram.
You can put power on the C147 wire going to the alternator after you disconnect C147.
You might want to check for power with the key in the run position at disconnected C147 before doing anything at the alternator.

C147 Location:

C142 Location:

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