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Hi, I’ve had this problem ever since I rebuilt the engine and I’m stumped, I got a new voltage regulator, new alternator, and new belt and I’m still only getting 12.3 volts. I’m at the point where I’m thinking it could just be the belt slipping on one of the pulleys but I’m not sure, any help would be appreciated, thanks
Is this measuring the voltage at the battery with a voltmeter while it's running?
Is the battery draining while driving? If it's not charging, your battery would drain and the engine would continually get weaker and then die within about an hour or two of driving.
Does the voltage increase if you increase the engine RPMs?
Do you have a bunch of aftermarket accessories on the truck that are pulling extra amps? Big stereo, high output headlights, sub, electric fans, etc? The stock alternator was only rated for something like 40 - 60 amps, so it can quickly get overtaxed with today's addons.
I was having issues with only getting 12 - 12.5 volts. I have a voltmeter in the cab and would see that it would sometimes get up to about 13 while driving, but could get as low as 11.5. It was enough to keep the battery topped off, but it was never a very good charge. I finally swapped out the old 1G alternator setup for a 3G, which puts out some 130amps. I know have 14 - 14.5 volts all the time, even at idle. Just too much draw on the old system.
Thanks for the reply! Sorry i didn’t respond for a while, pretty much the only thing that would drain it that I’ve added on is a new radio but that’s it, when it’s running at idle it gets 11.6 volts and that by check it with the multimeter. Positive on alternator positive stud and negative on battery terminal.
12.3 is no bueno. Turn on all the lights and heater blower fan to load up the alternator. Spool up the RPM to cruising speed around 2300 and hold it there. Measure voltage at the battery posts. See what you get. 13.8 to 14.2 at 77° F is what you want to see at idle, roughly, with no lights on. "New" doesn't mean any good. I think they just rebox defective units and resell them till they stop coming back.
If the ground cables and battery cables are original, or old enough to buy tobacco they should be replaced. Just a tiny bit of corrosion, hundredths of an ohm, too low to measure, will cripple the starting and charging system. It will still charge but so slowly you'll have to drive to Montana to get it done.
Google the 3g alternator swap. For like 50-100$ you can swap in a newer 3g alternator from the junkyard. They put out way more amps at idle, some models up to 130amps total. They have internal regulators and just way better overall.
Start by checking that you have good grounds all between the block, battery and body. Most parts stores will load check your battery for free just bring it to the counter. Do that before spending money on parts.
I had pretty much the exact same problem happened literally 20inutrs down the road, in a rain storm on my way from VA to SC after I bought the truck. Wipers and heat on wipers got slow lights dimmed out then the truck died. Was spitting out 11.5-12.3v. I made it home eventually by stopping and charging the battery. Pulled it in shut her down and she wouldn't crank back over.
Replaced the battery cable this helped a bit. New starter selenoid for giggles.
Found two issues eventually that seem to have stopped the issue. 1) my fusible link to the starter selenoid was bad (I have a metric ton of it if you need some) 2) there are a couple splices between the 1g alternator and the starter selenoid. They were all corroded, junky and half falling apart. Wires were nicked, strands cut etc. I replaced the wire and splices from the alternator back and got my voltage back up.
Lots of times, those wires and components get overlooked.
Josethef100, which 3G did you get?
Keep in mind that it does take some wiring change to get it installed. Plus, you need to increase the gauge of your your alternator to battery cable or you'll melt the stock one.
Lastly, if you have a V-Belt, you have to run two belts on it if it's the 130amp version. 1 belt just won't be enough.
I just did this conversion in mine a few weeks ago, so let me know if you have wiring questions and I can take pictures.
Thanks for all the info! I looked at the wiring several times but it all looked fine but I’ll replace some just Incase, I bought a 3g alternator for 93 or 92 300 I believe and it’s 130 amps, I should be good as for the wiring since I found a good diagram but thanks
I found numerous wiring diagrams, and they all showed how to wire it into the charging system, but not how to integrate it into the vehicle.
Not sure what year yours is, but in mine, the stock alternator wiring is integrated into the wiring that goes into the cab and powers the interior, as well as the key-on power. Almost none of the wiring diagrams include this aspect.
Oh, and DON'T hook up your current ammeter or you'll melt it.
There are some writeups on how to convert it to a voltmeter, but you'll have to look those up. I didn't do it yet, since I have a voltmeter on my Sniper EFI handheld, and that works great.
It's required if you want to know if it's charging or not. Otherwise, you can just leave the wires clipped and dangling, like I did. But, then, you meter in the cab won't move.
So, not required, but useful.
The big yellow wire is original to the vehicle. It normally went into a wrapped cluster of wires, if I remember right. I cut it and put an end on it so it could go onto the post on the solenoid for positive battery power.
You can see it going to the plug (that you should currently have). That plug goes into the cab wiring, etc.
The red and yellow wires are for the ammeter, and I just have them clipped. I think you can look up "3G install ammeter to voltmeter" to get some info. There's also a place that you can ship your ammeter to and they'll convert it to a voltmeter for you.
The new system just has too many amps and will fry it. Last thing you need is a fire of some sort, so either convert it or leave it disconnected.
The green/red wire goes down to the 3G alternator. Mine was green/red on the alternator wiring too, so that made it easy to hook up.
