Based on what you posted and where the wires go and come from sounds right.
Today I checked my 81 as it was not charging but I did have wires crossed at the ALT. S & F where crossed.

That nasty looking splice I am going to say is factory as I have seen them like that on other makes.
Yes I would cut that out and get to good clean wire and solider it all back together.
I would then use liquid electrical tape, it is a brush on tape, to seal it up as you cant get srink tube to fit / seal it.

Now you did not say if the system is putting anything out?
On the older cars / trucks everything turned on, heater or AC if you have it on full, head lights on, radio on.
Take a voltage reading at the battery at idle. You may have 12.5 to 13 volts. Now bring the RPM up to 2000 RPM and see what the volts are, should be 14 to 14.5 volts IIRC.
If not then you have an issue some where.

Motor off remove the regulator plug, start motor and with a jumper wire from battery to the "F" wire you should hear the motor slow down a little and the ALT work. Check the battery volts and it should be way high.
If volts are high ALT is good and regulator needs replacing.
If not high ALT is bad and needs replacing. I like to replace both the ALT & regulator at the same time to be safe.

Now the ALT can put out the right voltage but still drain the battery. A diode, 1 way check valve for electric, is bad and letting the volts go the wrong way when it should not.

Another thing is a drain on the battery when the truck is turned off.
Using a test light remove 1 of the battery cables, I like the NEG one. hook the test light between the cable and the battery, everything off & doors closed you should not have a light.
If you do depending how bright will tell you how much of a draw.
To see if it is the ALT because of a bad diode remove the wire off the back of the ALT to the BAT. post, light should go out if the ALT is bad.

If not the ALT start removing 1 fuse at a time checking the test light and what ever one is pulled and the light goes out is the area you need to look for the draw.
Dave ----

 

Dave,

As always, thank you. I'll give this a shot. I've had difficulty finding a fuse panel diagram for my specific vehicle as the cover was lost a long time ago. Do you have this by any chance?

 

I have not looked at mine that closely but the old boxes did not have covers and the markings for the fuse was just below it or next to it.

Next time up in the garage I can check mine over to see how it's marked.
Dave - - - -

 

The "S" wire going to the regulator is the one that brings the alternator "online" to charge, and "offline" so it will not run down the battery. See if you have voltage on this wire all the time. If you do, that is a problem. If you only have voltage on this wire when the key is in run, then that is correct. The only other thing that could be running your battery down is a bad diode in the alternator, or you have another drain in the system somewhere. You can use a testlight and then pull fuses to find the drain if it's elsewhere.

Here's how to use a testlight to check for a battery drain.



If the "S" wire checked out ok, you can hook the testlight up like above, and if it glows bright, you can pull all the wires off the alternator. If the light goes out, you know it's the alternator causing it. If it still glows bright, you know the problem is elsewhere in the truck.

 

Thanks Dave. I'm really lost in the sauce when it comes to electrical trouble-shooting. Could you explain to me how I can Just test the "S" wire?

 

Sounds good, I appreciate it. I'm going to run through all your tests and I guess worst case scenario if I cant find a diagram I can just trace wires back to their source if it ends up being a draw that I find in the fuse box.

 

You are going to need a testlight or voltmeter. Harbor Freight is a good place to pick these up cheap. I recommend at least the testlight. When you get it you will clip the one lead to the battery negative terminal, and then touch the probe to the + terminal to make sure the light is working. Then unplug the regulator plug and probe the s wire. With the key off the light should not light. With the key on, the light should light.

 

Remember when testing for a battery draw don't forget to close the door because the inside light(s) will make the test light light up.
Also does the truck have a glove box light? If so make sure it is off. Sometimes there is so much junk inside the door does not close all the way and the light stays on.

As I think it was posted if you pull all the fuses out and still have the light pull the wires off the ALT.
Dave ----

 

 

Good work on finding the bad regulator and getting it charging again.

On the ALT battery lug, I believe it should not make a difference how tight it is.
Now an ALT can still charge and have a bad diode and drain the battery.

I wonder if you don't have that battery lug tight enough that is also not charging the battery?
Have you checked if it is still charging before you closed the hood for the last time?
If you have not done so check that it is charging and if it is you are good and enjoy the truck.
If not tighten that lug and test if 1- it is charging, 2- it does not have a drain.

If charging and draining time for a new ALT also.
Dave ----

 

He my be putting a certain amount of torque on the nut, and that is affecting the diode pack. I have never had one of these 1G alternators apart, but it seems the diode pack is in the area of the output stud. He may indeed have a intermittent diode failure, and the nut is affecting it.

 

With all this talk of battery drain I was out doing things to mine and put a volt meter across the battery & cable, test light is in my electrical bin and did not feel like digging it out.
Any way I had 8 volt draw Not Good! And I don't have anything hooked up, all lights are out, other than to start it to move out & in the garage.

Because the truck is not on the road I disconnect the battery when it sits. Just gives me something else I need to look into.
Dave ----