Let me first start by saying I know there are a TON of posts about this type of issue. I have read many of them and followed a few of them in an attempt to diagnose and solve my issue. Here are my symptoms and what I have tried so far.

Symptoms:
Battery voltage reading car off: 12.67
Battery voltage reading car on, no load (lights off, radio off, fan off): 12.01
I didn't even bother putting a load on the battery as you can see the alternator is not charging well enough.

Attempted Fixes/Diagnosis:
Alt was purchased on June 1 of this year brand new, it is the alt from a 2000 Chevy S10 with the V6. I took it back to the parts store to have them test it (off the car) and it passed with flying colors, 14.92 voltage output. Not the alternator
Battery was purchased from same store 2 days prior, the previous alt killed the battery and it was beyond saving so a new battery was needed before determining the alt also needed replacing. The battery holds a charge of 12.67 overnight with no issues. Battery not the problem.
Checking for a short was the next thing I found on the forums. So i got my multi meter and also purchased a 12 volt test light.
At first, the test light showed a short was present. I pulled each and every fuse and relay from the dashboard side panel, then from the inner most fuse box under the hood, then finally the second fuse box under the hood. I was unable to get the light to shut off. I also disconnected the stereo equipment in the trunk, but with no changes.
I then hooked up the multi-meter and found there was no amp draw, (0.01). I replaced each relay first, checking for an increase in draw each time. Then replaced each fuse. I was unable to get an amp draw above 0.04, which seems pretty standard for "everything is ok". I then hooked up the test light again, this time, the light did not come on leading me to believe that no short exists. With that, I started the car up and checked the voltage on the battery. It was still 12.01, not nearly enough to maintain a charge.

So now what? Is there a wiring issue under the hood? Could the harness itself be bad? I am starting to think that this might not be something I can diagnose and fix myself :/

Anything helps. Thanks.

 

I didn't see where you've check to make sure you had good clean grounds or tried replacing your wire leads.

 

True I did not mention that. I am not sure exactly what lead wires you are referring to, reading on here it sounds like "lead" wire can be anything from the terminal connecting wires to any wire that takes positive current to the cabin.

As far as the grounds are concerned, they might be the issue. The hot wire that runs to the post on the back of the alt is on fire, melting its way through plastic conduit and also starting in on the alternator shield itself.

This wire getting unnecessarily hot makes me think that something is getting grounded when it shouldn't, which is what lead me to look for a short, which I was unable to find. Could any of the grounds cause this? I don't know why this would start happening all of the sudden if it was a ground wire, but I am definitely up for doing some investigating.

 

Looks like that wire has suffered some visible damage and probably additional heat related fatigue which might go beyond what is visible. In addition to solving whatever problem has led to this overheating, that wire should also be replaced.

Maybe this is too obvious, but was the melted wire touching anything that it shouldn't have been? Perhaps a small bit of missing insulation has resulted in a self-worsening problem.

But then, the suggestion about checking grounds is a good one as well. Looking at the engine bay picture above I can see several non-stock items, so the car is obviously modified. How much of the engine/engine bay has been taken apart at some point? Perhaps some key grounding points have been marginal for quite some time, and general corrosion/operational vibration has finally taken them from marginal to unacceptable.

What was the very first symptom? Just poor charging? Or did something else occur (or was some other work done) immediately prior to whatever alerted you to the fact there was a problem?

I don't necessarily trust the alternator test machines at local parts stores. I've gotten several false "good" readings before, only to have the alternator fail to charge once it's fully heated up during normal operation. But it sounds like your charging issue begins from the moment the engine is started, even cold, so this is probably not your issue - not to mention the melted wire.

The behavior of the test light is odd. Do you happen to have another one you can use to verify? I don't know why it would continue to indicate a problem with everything disconnected, but then stop indicating a problem once everything is reconnected.

 

the entire engine bay has been empty at some point. Original engine threw a rod so we built a better one to put in. The guys that did the work did tell me they needed to rebuild my wiring harness, but I took delivery on the vehicle almost a year ago. No charging issues were present then, if they were, they didn’t show. Recently the transmission came out for a rebuild/upgrade. Only after putting that back in did I start to notice the charging problem. That was May 23rd this year. The battery bit the dust on the 30th and the new battery and alternator were purchased on the 1st of June. Since then I have not been able to get a good multi meter read :/

The center console comes out when the trans is removed, so I can open that up and check for randomly grounded wires. I will definitely be replacing the output wire today. Hoping the output wire was the original issue and maybe then the issue just goes away.

 

I was referring to the grounds and your power lead from the alternator to the battery but I think you may have found an issue as the power wire got hot and melted away the insulation and like RPM WS6 stated this can weaken the wire due to the heat. I see the alternator was relocated to the passenger side so did the leads stay the same length or get lengthened thus making the current have to travel further.

 

Quick update. I changed out that lead wire, increased the gauge as well. Went to a 4 gauge wire, the previous one was at MOST a 6, but likely closer to 8 or 10. I am now getting 14.6 volts at the battery when the car is idling, and 14.2 volts when i turn the radio way up, get the lights on and the cooling fans running. I want to say the issue is fixed, but after idling in the driveway about 6 minutes while I waited for it to get to temp and did the testing, the alternator got VERY hot. I should go buy a thermal gun and hit it to see what the temp was, but I was testing the heat by touch and it felt hot. I also noticed the gauge in the car doesn't point to 13 (straight up) which makes sense because it was getting over 14, but at the same time it straight up is the 'operating norm', then I think I should do something about it.

Thoughts guys?

 

Sounds like you found the issue and your voltage gauge should read just past 13 with a charged battery. At least that's what it says on my voltage gauge when I'm out driving.

 

14.6 volts is too much though.

 

So what do you do about it? Why is it too much?

 

You see 14.6 with a radio, vehicle lighting, AC and fans running? Yea, maybe too much. I see that at the battery before turning those things on and about 13.8 with them all on.

Have you checked continuity and voltage on Terminal F and Terminal L at the alternator?

Rick

 

Hey Rick.

it’s actually 14.6 with no load. Once everything is on and running it comes down to 14.2. I don’t have AC but I have electrical radiator fans. I have not been able to check continuity from F and L terminal. I was also going to try and check the current on the alt while it’s running.

 

I checked mine this evening with a multi meter and I'm reading 13.6 with the engine idling. My thinking is that too much could damage the battery and its possible that your alternator could still have an issue. Are the ones out of S10 trucks the same as the 4th Gen V8 cars?

 

The mounting brackets are a little different which is why I use the S10 one. But the stock Fbody alt is rated at 102 amps and the S10 alt at 105. Not a big enough difference to consider it being an issue. Definitely don’t want to burn anything up. From what I’ve read anything from 14.4-14.7 at idle with no load is acceptable. Then anything above 13.7 under load is fine. Just worried about the temp of the alt, but I should get a heat gun and see what the temp is.

 

This seems to be the consensus for what your alt and battery should be doing. This is the 3rd video I have seen that uses these numbers. I think I am going to be ok for now. If the alt burns up I can address that later.

 

I don't see anything wrong with those numbers; keep in mind you also upgraded the wire gauge so that should decrease the voltage drop (hence a slightly higher number at the battery than a totally stock setup). Plus, you didn't mention how long the engine had been running when you recorded those numbers - mine always reads higher (load or no load) until after the entire engine bay is fully warmed up. Lastly, I wouldn't worry too much about the alternator "feeling" hot unless something is melting again, and/or you see numbers that are way out of line with an IR thermometer (I've honestly never checked alternator temp, so I'm not sure what is "normal" but I wouldn't expect it to be drastically hotter than any surrounding metal material once everything is fully warmed up).

 

Thanks, I was thinking along these lines as well. If it falls apart, I'll just figure it out then
Doubt it will give me any trouble anymore tho

 

Quick update. Everything is going great. I was even able to get ahold of my shop guys and ask them about it and they said "14.6 no load is perfect". Sounds like everything is all good

 

my truck alt runs 14+ all day.......not a pro

 

UPDATE:
Everything is running great! Using the alt from a 2000 S10 with the V6 (fitment reasons) and charging issues have disappeared once that wire was replaced and upgraded. Thanks for your help all