Hey guys, needing some help regarding my alternator on my 94 Ram 2500 5 speed 360. Unfortunately, for everything to make sense, I have to give some back story...
This past June, I changed my front shocks, I ran a cigarette lighter powered work lamp for about two hours while I changed them. That ran my battery dead. Seemed odd, but jumped it, and drove 20 minutes to work. Then started the truck, drove a few blocks, shut it off, but left the hazzard lights blinking for about an hour (normal occurance bc of my work). When I went to restart it, it barely turned over twice. Had to jump it. I let it idle for an hour. After that, I didn't have any problems that day, but I took it to Orileys that evening, and had them test my battery. They said it passed, but that my alternator failed the charing test. I didn't have the money at the moment for a new alternator, and it had worked to start the truck probably 10 more times that day, so I put it off. Talked to a buddy that weekend who's a diesel mechanic, he tested my alternator with a voltmeter, and said it was just fine. I had one more dead battery from about half an hour of running my hazzards, so I decided to put a new battery in it, and swap the possibly bad battery over to my prodject truck (after a little testing, I determined it was a bad battery). Somewhere along this journey, I realized that my voltmeter in the truck was reading a little higher than normal. I think it started when I put the new battery in. I didn't think too much of it, since, it is a 90s Chrysler product after all, and my buddy had said the alternater was fine. About a week ago, I relaghed this series of events to a different friend, who is also a mechanic, and he said I should take it to a different parts store, and have them test it as well, just in case. He suspected that it might be over charging my battery. I took it to Autozone this time, and they said it failed the charge test. I bought a rebuilt alternator from them. I was going to put it in today, but saw that the new alternator had a sticker on it that said it didn't have a built in voltage regulater. Correct me if I'm mistaken, but isn't it a voltage regulater that would have failed on my current alternator, since it definitely produces enough power, since I haven't had to jump start it since I put the new battery in, probably 2k miles ago? I'm really confused at this point... did they give me the wrong alternator? Did something else fail other than an internal voltage regulater? From a little research, it looks like our trucks have voltage regulaters that are built into out pcms... has my pcm voltage regulater failed? Could that be mistaken for a faulty alternator by an alternator test tool?
Thanks in advance for any help y'all have! I'm at a loss right now, and just don't feel like putting a new alternator in, if that's not going to fix my problem...
Courage

 

I'm trying to sort through the massive wording here. Is the truck running okay and charging now? The PCM is the regulator on these trucks. I have seen weak batteries work okay but when deep discharged, reach the end of their service life quick. Were the alternators bench tested or tested on the vehicle with a test system? I've had alternators test bad at the parts store but my tester said it was good. A local auto electric shop tested it and it was good there too. That alternator is running strong nearly a year later.

The first thing I would do is make sure you have a good strong battery and the battery cables are in good shape. Check both ends. They can look good at the battery but be corroded at the frame or destination connection.

It looks on your gauge the alternator system is working. What does a volt/ohm meter read when it's running?

 

I'm sorry! That really did turn into a long, wordy post!
Yes, the truck runs, and seems to be charging just fine. I've not had to jump it since I put a new battery in it, and I've left my lights on once even, with no problems, not to mention the numerous times I've recently jumped other people's cars with it.
The alternater that's on it was tested by both Autozone and O'Reillys while in the truck.
Yep, good strong battery, and battery cables, at least on the battery side. I'll check the other ends though.
I don't have access to a voltmeter atm, but when my diesel mechanic friend checked it, i believe it was reading 15.5 volts. Could be wrong though...
Basically, my only concern is that it's overcharging my brand new battery....

 

It's a touch high but with a new battery, you might have plenty of voltage but the amperage saturation is still building. Invest in a cheap volt/ohm meter. You can get really cheap ones under $10 at Harbor Freight, at least for now. A basic digital is all you need unless you work on 1995 or older Ford products. A fully saturated battery will read 13.5 to 14.5 while the engine is running. About 12.3 to 12.6 when at rest. Saturation is basically building your cranking amperage. 16 volts and more would be an issue.

 

In a 94 the voltmeter in the dash is an analog gauge measuring the voltage between ignition power and ground. In the picture the needle sits in the perfectly normal position at around 14.2 V. Your friend might have measured directly at the alternator with a pretty much dead battery which would explain a higher voltage. The PCM reads voltage internally and not at the alternator or the battery.

 

Thanks guys so much for your help!
I'll pick up a voltmeter tomorrow. I do actually have an 89 f150, so I'd want to get one that will work with pre 95 Fords. What style would I want to get? Is it a bad idea to drive it tomorrow to go pick up a voltmeter? I parked it since the second place said it had a bad alternator...
Also, I've never used a voltmeter before, although I've seen them used plenty... know of any good write ups on the specifics of how and what to check?

 

Any Digital Multi Meter (DMM) will work, they are universally useable for all sorts of things not only automotive. If you have a Harbor Freight nearby they have a dirt cheap DMM for less than $10, a better one for $20. Don't spend more than $30 unless you want to upgrade to a clamp style device that can measure current by putting the clamp around a wire. That can tell you how much current is going in/out of the battery (different from the voltage at the battery). Google or maybe "the AI" has plenty of info on how to use a DMM to check charging.

 

Your original problem was a failing battery, not the alternator. If everything is working as it should now, and you aren't having any problems, the, you don't have any problems.

 

Did your idiot light come on? The volt gauge is not always accurate. And the short drive may have not been long enough to fully charge the battery. If you don't have any issues with the new battery you don't have a problem.

 

Normally I use a digital meter. However, with the OBD I system on Fords, you ground cross two terminal and watch the sweeps of the volt meter. Digital meters don't work for this. I've got a specific reader from back in the day that has a light you count the flashes on. I haven't seen one of those in years. You don't HAVE to have it, it's just easier on your Ford. Otherwise, a digital does just fine. See if you can find one with a sound alert for continuity. The meters usually come with instructions on their basic usage. Otherwise, you're on the internet right now, just look around. I often go to the U of Y to refresh mym memory at times. (Youtube)