Charging voltage @ 12.9ish at idle! 83 B2000 Sundowner

I cannot figure this one out; i have been up and down everything i can think of for weeks now. luckily i have a charger and my old battery as a portable jump-station if needed....

I have a number of electrical problems that may or may not be related.

first little thing is my running lights/dash lights blow their fuse often and definitely have a sporatic short someplace....

The big issue i am having though is that the battery is not getting a full charge; the alternator is a reman, replaced the other reman i had due to this issue on warranty but to no success.
At idle it runs about 12.6-12.9 volts and does not change muchat higher rpm; immediately after start up the battery light comes on solid untill i juice the gas once or drive off.

I replaced the battery recently, also a reman, but it seems to be fine.
I checked and rechecked every connection i can find; new terminals, cleaned grounds +dielectric grease, and checked fuses.

There seems to be a buzzing noise coming from a relay in the ignition wiring; i dont even know what it is called let alone can i find it at a parts stare; maybe a junkyard trip is in order.

Also i suspect the fusible link from Alt to Batt but it shows no resistance; the Alt works, it has been bench tested multiple times.

Thanks for throwing in your two bits!

Been a few years since I owned a first gen B. When you say the fuse shows no resistance, are you checking continuity or trying to ohm it out? The buzzing noise kinda reminds me of the buzzer that sounds when you leave your lights on or the key in the ignition when you open the door. Also that battery you installed, have you had it load tested? And after the truck runs a while is the alternator really hot to the touch? If the battery is crap (yes they can be bad from the factory) it will make that alternator work pretty hard to try and keep it charged, not I have not seen a battery draw an alternator down that bad but it is possible. AS far as the battery light goes after you crank it and have to gas it to get the light to go off that is common with some GM alternators that require a certain voltage to "excite" the alternator and make it charge, quite a few GM one wire alternators do that. I would double check that fuse using continuity if you haven't already done so and do a quick look on the wires that plug in to the back of the alternator and make sure they have good contact and aren't broken or touching any other surface that could ground them out.

Advances!
PARASITIC DRAIN!

Battery place measured the drain at ~2.8 Amps with a pick-up type deal....
Battery was FLAT dead today; two days sitting at 50-60ish degrees....

I pulled all of the fuses and a ton of ignition wires, switches, blower motor wire, and such but we could not find the culprit!
Could the trailer wires draw that much? I may take them out because towing is pretty much out of the scope of my truck.

Where do i look that is outside of the fuse box?
I do have wiring diagrams but translating it into what i see is hectic at best...

Next plan is to disconnect the Alt. and see if that does it (diodes or some such) but it is a new reman. and has been bench tested MANY times.

The trailer wires should have ZERO draw because they are not connected to any trailer.

Charge up the battery. Disconnect the alternator. Install battery. I'm thinking bad alternator.

You need to track down that short. Whenever somebody comes on and says that their running/parking/dash lights are blowing the fuse, 8 out of 10 times, it's because a "radio illumination" wire has been cut and left dangling behind the dash when a previous owner upgraded the radio and saw no need for that wire. It wasn't shorting anything out during the install because the lights weren't on. And maybe it didn't short for a long time but has since rattled loose and is touching the transmission tunnel or the dash framework. So that is something I would definitely check out. The other common issue is if somebody has tapped into the existing lights to run fog lights or something like that, and left some wires less than secure. I would closely inspect the wiring going to the parking lights. And as has been mentioned, to the rear for the trailer lights.

If you start the truck and then disconnect the battery, what voltage are you getting then? Your battery alone should be putting out the voltage you are getting now. If you disconnect the battery and then measure the system voltage (on the harness terminals), you'll be reading the alternator voltage without the battery being connected. If it goes up to the 13-14 volt range, then you'll know it was the battery dragging the alternator down. If you still can't get more than 13 volts (system/alternator) with the battery disconnected, then your alternator is weak. Pull as many fuses as you can but still have the truck running (battery still disconnected) and see if you can't get any more out of it. If it goes up significantly with fuses pulled, then it is something else dragging the system voltage down.

Charge the battery and take it down to the auto parts store and have them load test it. I have seen bad batteries as well.

Find out exactly what relay is buzzing. Get a picture of it and post it if you can. Somebody here will recognize it.

Solved it!

Alternator was shot!

So bunk parts are common i guess. that makes 2 warranty trade-ins thus far!
This new one does seem to perform much better than i can ever remember. Haven't taken the meter to the volts yet but in time....

Also found out that my multimeter does not measure amps at all, always reads Zero (yes i had all the plugs set right). but the bulb from the interior light was perfect for touching between the post and terminal for a second (i knew it was only 3 Amps from the battery-place testing it yesterday).

Are you sure that the battery is OK? Also, these typically have a fuse inside the multimeter for the ammeter circuit, and only can handle very small amount of amps. And good luck finding replacement fuse to fit (ask me how I know this).

If voltage across the battery is like 13.5 to 14 volts at like 2000 rpm, then it's charging, no need to do further testing at this point.

My battery is fine, and i am beginning to think my old battery is as well and that it has always been my alternator screwing things up.
As i have a stationary charger i have kept the old one charged up to ensure it doesn't go bad...

My truck has a spare battery-bay.....would it be worth it to throw another one in there?
Probably would not use an isolator (yet), just have a battery bank hooked so the starter draws on the ground from one battery and hot from the other battery....

As for the multimeter.....
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