Stranded, need alternator/ charging help

I installed a new alternator, like I have dozens of times before, and its not charging. I had them test it at the store before I brought it home, and tested fine. My battery is a few months old and shows 12plus volts on it own, when I run the jeep, it shows low 12s. The dash volt meter shows the same or lower.

Am I missing something. Is there an alternator charging fuse, and if so where? I thought 96s where internally voltage regulated, am I wrong? Is so where is it at? Could my battery be bad already? Going to get it checked today, because after that, Im out of options.

On a side note, I upgraded my cables months ago and did not install a fusible link.

From what you have posted it does sound like there is an issue. Using a good multimeter a fully charged 12V battery is about 12.7 Volts.

When running (charging) the system should be reading less than 14.7 volts but over 14V

Look at my response to your previous thread.

'96 alternators are regulated in the PCM.

When upgrading cables you do not use a fusible link, you use an ANL or Mega fuse. I thought you said you already have an ANL fuse and holder.

I believe the green wire from the alt goes to the PCM for the regulator circuit but someone can correct me if I am wrong.

The 4 gauge power output wire from the alt goes to the fuse then to the battery + or PDC +. It doesn't matter which but the battery is easier.

Pelican, is this a possible solution to my non charging problem? I am to delete the green wire, which is probably broken at this point, and put an anl between the hot wire from the alt and the pdc.

1. the dash gauge is notoriously inaccurate. Don't rely on it. Measure with a meter at the battery.

2. The alternator field is regulated by the PCM. The ASD relay feeds 12v to the alternator field via the dk grn/org wire. The PCM regulates the ground to the field via the dk grn wire. There is no need to change or upgrade these wires unless there is a connection or corrosion problem. The PCM regulates charge voltage based on demand, and battery temperature. This can vary from ~12.8v to 13.7v. You will never see 14.7v from a chrysler product. The important part is amperage anyway, and for the shadetree mech it's not cost effective to buy the equipment that can measure the true output.

3. All the output of the alternator comes via the B+ wire that routes to the PDC. It is fused inside the PDC with 2 40a maxi-fuses in some years, or, in the case of the OP's 96, a single 125a fuse in the pdc.) When you upgrade to a larger amperage output alt, the B+ wire should be fused appropriately for the alt output, and connected directly to the battery positive terminal.

As long as it is outputing more than battery voltage (12.6v), it is charging. It will charge more at higher RPM...this is normal and expected. You WILL NOT achieve maximum output at idle. It's not possible without overdrive pulleys.

A wire has to go to the PCM to regulate the alternator output. Do you have that wire connected? As I said, I think it is the green wire but not absolutely sure.

Not sure what you mean by delete the green wire, but don't cut it out and throw it away until we are sure what it's purpose is. There has to be a wire running to the PCM.

And yes, you put the ANL fuse between the alt and the PDC or between the alt and the battery if you run your hot wire directly to the battery.

Edit: Digger87 posted with good info in the meantime. Note that he also suggested running your properly fused hot wire directly to the battery from the alt.

Edit2: For anyone who might be confused, in the '93 for one, the maxi-fuses in the PDC are 60 amps.

Pelican said:

A wire has to go to the PCM to regulate the alternator output. Do you have that wire connected? As I said, I think it is the green wire but not absolutely sure.

Not sure what you mean by delete the green wire, but don't cut it out and throw it away until we are sure what it's purpose is. There has to be a wire running to the PCM.

And yes, you put the ANL fuse between the alt and the PDC or between the alt and the battery if you run your hot wire directly to the battery.

Click to expand...

addressing the bold type; there is no reason to install a fuse if the factory wire to the PDC is reused. And if the ALT is upgraded to a higher amperage, there is no reason to reuse the factory wiring as it will be underrated.

Digger, thanks for the response. My battery alone reads 12.6. When I start it up, it goes down to 12.1. When I turn on any accessories, it drops to 11.8 or so, no matter how high I rev it.

That being said, prior to the alternator going bad, when I upgraded my cables, my dash gauge was very close to what my multi meter claimed and still is. When I changed my cables, the dash and multi meter both read 14 plus.

I don't see a 125 amp fuse in the pdc, where the rest of the fuses are. Is it actually inside of the pdc? Thanks so much for your patience.

It doesn't look like a regular fuse. Where the factory black/white alt wire feeds into the PDC there is a metal strap that bridges across to the post where the wire from the battery terminal cable comes in. That bridge is the 125a fuse.

Is sounds to me like you need to troubleshoot the field wires from the ASD and the field control wire to the PCM. It may come down to a bad PCM as well.

MY 1996 XJ did not have that ANL type fuse on the front of the PDM. In fact it had only one bolt there and a blank space where the second bolt for the ANL fuse should go. It did have an 8AWG wire coming from the alternator which split into two at the PDM via 2 60 AMP large fuses.

When I upgraded the wires, I removed the OEM wire from the alternator and replaced it with a 4AWG wire and a 125 AMP ANL fuse in the front of the PDM.

On your no charge issue, probe to the small wire terminal closest to the wire that connects to the battery on the back of the alternator with the engine running using a volt meter. You should have about 12 volts there to excite the alternator. The other small wire next to it is the negative supplied by the PCM to regulate the alternator output. The alternator will not work unless these two wires are connected. They are on a single pod together with a larger wire that provide the alternator case ground. If there is 12 volts at this terminal then you could proceed to test the main output from the alternator (at the alternator) then at the PDM and fuses.

I have yet to find the 125 amp fuse. My set up is like listed above with two 60 amp fuses. We tested the field terminals and both were putting out positive current, 11.33 approximately, cant quite remember.

So, now what? Can I test the anl relay or is it even worth trying at this point. Is there a way to test a pcm? So I guess my worst case at this point is a possibly bad pcm.

Im beginning to get out of my depth unless you good gentle men have any other ways to diagnose whats happening, then my rig is gonna be parked to I can get it to an auto electrician.

Again, thanks for all of the help. This is the first serious issue Ive brought to the table and you guys have really come through for me so far!

bugout said:

I have yet to find the 125 amp fuse. My set up is like listed above with two 60 amp fuses. We tested the field terminals and both were putting out positive current, 11.33 approximately, cant quite remember.

So, now what? Can I test the anl relay or is it even worth trying at this point. Is there a way to test a pcm? So I guess my worst case at this point is a possibly bad pcm.

Im beginning to get out of my depth unless you good gentle men have any other ways to diagnose whats happening, then my rig is gonna be parked to I can get it to an auto electrician.

Again, thanks for all of the help. This is the first serious issue Ive brought to the table and you guys have really come through for me so far!

Click to expand...

I see reason for your XJ to have a positive on both terminals. According to the 1996 manual, the dark green and orange 16AWG wire is tied into the ASD (Automatic Shut Down) relay which provides positive to the ignition coil, fuel pump and others which requires 12 volts. The dark green 20AWG provides the ground path to the alternator field driver from the PCM. The PCM toggles this ground to regulate the alternator output.

Some time ago I had a charging problem and did a quick and dirty test to the alternator. I removed the field connector from the alternator and connected pieces of wire to the positive and negative terminals of the alternator as indicated above. The positive go directly to a positive source. With the engine running, temporarily ground the end of the other wire to a good source. With a good volt meter connected to the battery watch the voltage rise above 16 volts. Keeping the wire grounded for an extended period could easily see voltage upwards of 18 volts with a good alternator so use extreme caution.

I am assuming you have already verified you have a good connection between the alternator output terminal and the battery. Before doing any of this, you MUST verify that the connection between the alternator and the battery is very good or the results may be disastrous to the XJ electricals. If this test show the alternator to be good then proceed with the XJ wiring diagnostic. If a minimum of 16 volts is not seen, replace the alternator.

I thought the alternator was already proved to be working when on the bench, but Ill take your word for it.

This is getting too complicated for me and my Harbor Freight multi meter.

So, the asl relay isn't the problem because the jeep starts?

So I have to figure out if the computer isn't telling the alternator to charge?

If that's the case, am I looking at a new or used ECU or can an external voltage regulator be fabricated?

techno1154 said:

I see reason for your XJ to have a positive on both terminals. According to the 1996 manual, the dark green and orange 16AWG wire is tied into the ASD (Automatic Shut Down) relay which provides positive to the ignition coil, fuel pump and others which requires 12 volts. The dark green 20AWG provides the ground path to the alternator field driver from the PCM. The PCM toggles this ground to regulate the alternator output.

Some time ago I had a charging problem and did a quick and dirty test to the alternator. I removed the field connector from the alternator and connected pieces of wire to the positive and negative terminals of the alternator as indicated above. The positive go directly to a positive source. With the engine running, temporarily ground the end of the other wire to a good source. With a good volt meter connected to the battery watch the voltage rise above 16 volts. Keeping the wire grounded for an extended period could easily see voltage upwards of 18 volts with a good alternator so use extreme caution.

I am assuming you have already verified you have a good connection between the alternator output terminal and the battery. Before doing any of this, you MUST verify that the connection between the alternator and the battery is very good or the results may be disastrous to the XJ electricals. If this test show the alternator to be good then proceed with the XJ wiring diagnostic. If a minimum of 16 volts is not seen, replace the alternator.

Click to expand...

This is called "full fielding" the alternator. If you can get to the field winding control connection you can ground this without removing all the wiring and acheive the same result.

If you're feeling confident enough, backprobe the alternator control circuit at the pcm to ground. If it charges @ the 16v spec, the harness and alternator are good and you need a PCM.

Is there a way to run an external voltage regulator, either bypassing the pcm or without screwing it up?

bugout said:

I thought the alternator was already proved to be working when on the bench, but Ill take your word for it.

This is getting too complicated for me and my Harbor Freight multi meter.

So, the asl relay isn't the problem because the jeep starts?

So I have to figure out if the computer isn't telling the alternator to charge?

If that's the case, am I looking at a new or used ECU or can an external voltage regulator be fabricated?

Click to expand...

Don't trust your Harbor Freight meter to tell you much. I've bought many to scatter around my vehicles. Then, to better test a boat motor issue, I bought a $40 analog meter. The HF ones were more than a volt off. Only trust it to tell you that you have more or less than you had before.

That said, with it running you still should see more.

Not sure if this is safe, but it seems like you could ground the field wire to see if the alternator went to full charge. I wouldn't do this for long.

OK, so help me understand this. I leave my Alt to PCM connected. I remove the field coils connection. Then I ground out one side of the field coil, (does it matter which?). Do I ground the original alternator ground also?

If somebody could clear this up for me, I would appreciate it. I do good with pictures.

Apparently we are sending you into deep water here and you aren't swimming. You are flip flopping around like a fish out of water. We are posting as clearly as we can but you aren't comprehending it well.

It's important that you know what you are doing, or it's time to give up and pony up for a mechanic that does.


Verify the connection (ohms test) the dark green wire from the alternator connector to the PCM connector. (both unplugged)

If that is ok (.5 ohms or less), then reconnect everything. see **

If it not ok fix it. and verify the repair

** to full field the alternator to test it's output, ground the dark green wire with the engine running. You should see the results techno posted.

bugout said:

Is there a way to run an external voltage regulator, either bypassing the pcm or without screwing it up?

Click to expand...

no

bugout said:

I have yet to find the 125 amp fuse. My set up is like listed above with two 60 amp fuses. We tested the field terminals and both were putting out positive current, 11.33 approximately, cant quite remember.

So, now what? Can I test the anl relay or is it even worth trying at this point. Is there a way to test a pcm? So I guess my worst case at this point is a possibly bad pcm.

Im beginning to get out of my depth unless you good gentle men have any other ways to diagnose whats happening, then my rig is gonna be parked to I can get it to an auto electrician.

Again, thanks for all of the help. This is the first serious issue Ive brought to the table and you guys have really come through for me so far!

Click to expand...

Bold: OK so, yours has 2 60 amp fuses. It doesn't use the 125a. Its moot anyway as I thought you upgraded the batt wire to connect directly to the battery? no?

Bold red: the dark green wire should not have the same voltage on it as the green/orange wire. there is a problem between the alternator and the PCM or the PCM is no good.