Charge system issue. (1 Viewer)

Joined
Jul 25, 2019
Messages
424
Location
Maine
Hey all I'm in need of some assistance. My dad has been in and out of ICU with heart problems so I'm blaming anxiety for my brain not getting this figured.

Here's the deal:

My charge light was on earlier this morning. So figuring a bad alt. I put a charge on it for 15 mins with charger and drove to my shop. Sure enough via multimeter, I got battery voltage at alt output, ~12.3 v. Easy enough as I have a parts truck with low miles and a known working alt. as of a few months ago. So I swap it out and I'll be damned it's the same issue.

Here's what I'm working with:

Truck is baselines to the max
New agm battery
I had rebuilt the first alt. 3 months ago and is oem
Swapped alt. Is also oem
Charge fuse good
New fusible links last week
All connections tight and clean

Now in looking at the FSM diagram it's telling me I should have 0-4 volts at the black wire with ignition on. I have 12v at all terminals with ignition on and that has my head aching. Any help here would be great.

I work on cars everyday so coming in for a question like this really tells me my head is in a bad place.
 
Joined
Jul 25, 2019
Messages
424
Location
Maine
PXL_20201022_170447850.jpg



So I just popped the rear cover off my original alt. Apparently my brain is more off than I thought as I clearly did not rebuild this alternator as I said previously. One of the terminals to the regulator is melted to hell. The new alternator I just looked at and didn't end up like this yet but was very hot after only a couple mins of running. I'm fearing that whatever happened is either because of a wiring issue, or this issue has caused wiring damage hence the spare alt. Not working either. 🙄🙄
 
Joined
Jul 25, 2019
Messages
424
Location
Maine
If you only have 12.3 V, I would look at the battery. Possible a dead cell and causing shorting.

Good battery is 12.6-12.8V. Charging should be in the 13.5-14.8V range.
Battery is a 3 month old duralast agm. It was keeping me driving with no issue despite non charge of alternator. I've got it on a charger now to see what it does.
 
Joined
Dec 8, 2006
Messages
9,438
Location
New Jersey
 
 
First thing I would do is verify fusible links with a meter.
Next, verify the actual alternator output on the back of the alternator lug.
 
Joined
Jul 25, 2019
Messages
424
Location
Maine
Fusible links are new and all independently metered out to .5 ohm end to end. Spare alternator is now removed so I'm going to have the parts store spin it up for me later. Going to see what charge the battery holds here in a while.

Wiring close to alternator is pretty toasted and hard. Tough to say if recent or not but a good bit worse than I'd hope to see.

Any input on why FSM calls for 0-4 v on pin 3 of the connector and I have 12?
 
Joined
Dec 8, 2006
Messages
9,438
Location
New Jersey
 
 
Fusible links are new and all independently metered out to .5 ohm end to end. Spare alternator is now removed so I'm going to have the parts store spin it up for me later. Going to see what charge the battery holds here in a while.

Wiring close to alternator is pretty toasted and hard. Tough to say if recent or not but a good bit worse than I'd hope to see.

Any input on why FSM calls for 0-4 v on pin 3 of the connector and I have 12?
Did you verify fusible links before or after this problem?
Pin 3 of the alternator connector should be constant +12 as it comes from fusible link AM1.
 
Joined
Jul 25, 2019
Messages
424
Location
Maine
Links were given the most scrutiny after this last teardown. So they have been fine all along. I had no faith in finding anything but I did just do surgery on my harness from alt to battery. All seems well. The insulation all needed refreshing anyway so no time wasted there.
 
Joined
Jul 25, 2019
Messages
424
Location
Maine
Depending on perspective I may be confusing pin 1 and 3. You are correct though. Black wire constant 12. I am getting 12 on all 3 with ign on.

My battery appears to be holding 12.9 at rest after a 20 min charge.
 
Joined
Dec 8, 2006
Messages
9,438
Location
New Jersey
 
 
Links were given the most scrutiny after this last teardown. So they have been fine all along.
You're missing my point. The output of the alternator passes through FL Main. If there was a short in the system, then one of the FLs would let go.
Just because they were good does not mean they are still intact. That's what fuses do for a living.
 
Joined
Jul 25, 2019
Messages
424
Location
Maine
I get what you mean about that. I was saying that the links are good NOW, and I thought you were just questioning whether I checked them before changing the alt but not after and having the same issue.

At this point I'm leaning towards my initial alt s***ting the bed, and despite my spare one working a few months ago it is miraculously also bad and getting a new one will have me good? 🤷
 
Joined
Jan 5, 2017
Messages
2,573
Location
Charlotte, NC & Alexandria, VA
Seems like you have talked yourself into the "keep changing parts until the problem goes away" option. I tend to keep looking for the root cause until I find it, but both are valid paths to a solution. You pay for both; one in time, the other in money. And time.
 
Joined
Jul 25, 2019
Messages
424
Location
Maine
I've only changed one part. Also I did get confirmation this afternoon at my local starter shop that the second alternator was not working as well. Weird but not as weird as some stuff I have happen. Ordered a new one for Monday.
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top Bottom