(I'm posting this here so it will be easier to refer to, rather than re-typing explanation into various threads that need the explanation.)

Here's the 22RE-liable schematic:


Close-up of alternator pin-outs is here:


White "B" wire (heavy gauge) to the 80amp fuse
This is the battery charging wire.
From FSM:
With engine from idle to 2000RPM, Voltages at B should be:
13.9 to 15.1 V @25°C (77°F)
13.5 - 14.3V @115°C (239°F)
Not sure which temp it is. Could be battery temp. It affects electrolytic process.

WITH B-WIRE DISCONNECTED, measure resistance from screw terminal to ground. You should get Very high reading. Lots of Meg-ohms (Sorry I forgot how much mine read). If low, suspect bad rectifier (s).

White "S" to the 40amp (always-on) fuse
Tt should read as close to battery voltage as possible. This senses actual battery voltage and should be connected as close as possible to battery positive. It is merely spliced with the B wire near or at the junction of 80-Amp fuse and 80-Amp fusible link wire. Low "S" voltage means battery needs more charge so the regulator would increase output voltage. If "S" wire and or connection is bad it could lead to overcharging and charge fault error light would come on.

Red "IG" to the Engine fuse
This provides field current to "seed" the charging. This should have steady 12V when ignition is on (coming from Engine fuse). If no 12V here or if this voltage is erratic or engine fuse blows, trace wiring back to Engine Fuse, to "E" battery positive wire from fuse block, and verify that your backup switch or wiring is not shorting to transmission body as shown here.

Yellow "L" to the Charge Warning Light
This should be near +battery voltage when alternator is working properly (B voltage 13.5V-15.1V). If there is a charing fault "L" will go low - approaching zero, and provide ground to negative side of the Charge Light causing it to come on.
(Unfortunately, it also provides ground to Brake Light and A/T Oil temp light- making it confusing to many.)


Most accessible place to measure "L" voltage is here:




ALTERNATOR HARNESS AND MORE VOLTAGE TESTS OF NORMALLY-FUNCTIONING CHARGING SYSTEM:

I use the terms "inboard" and "outboard", instead of left/right or passenger/driver side for consistency, no matter which side of the engine compartment you are measuring from, no matter whether you're on Australia or the U.S., and even if you're in same resting position as Adam Ondra (LOL!)

Here are expected voltage readings at the two pins of the Charge Fuse on a normally-operating charging system of a 1986 Toyota MoreFunner with Charge fuse removed.
Correct, the charging system does not rely on the charge fuse in order to work. The charge fuse simply creates a connection between the "charge" fault light and the "L" fault indicator wire of the alternator.
Excitation is provided by "IG" wire from the engine fuse.


PROBING THE CHARGE LIGHT FUSE WITH IGNITION ON AND ENGINE OFF.
This simulates a charge fault condition where "L" signal is low or close to zero.


NORMAL CHARGING CONDITION WHEN ENGINE IS RUNNING

My turn to have charge fault light intermittently coming on.
Finally I was able to stop while it stayed on and verified that the system was overcharging (17Volts).
Problem Description:
1) OReilly charging system checker verified all good - test was done when not in fault condition.
2) Condition seemed to happen at higher RMP. When alt was rotating faster and there was more engine vibration. (Video taken while parked and parking brakes on):
YouTube

Hypothesis:
Based on (1), If purely electronic problem - say component values/characteristics in regulator has changed, it would be less likely to be intermittent, and should always happen when I rev up the engine.
Based on (1) and (2), more likely a connection issue, or loose component in regulator.
Intermittent connection in "S" pin of alternator would make it think battery needed more charge so it bumps up output, then realizes something must be wrong because bumping up voltage does not fix anything. Charge fault light comes on.

Verify:
"S" wire was OK up to the front of the alt connector. It always had batt voltage.
There is no way to check if regulator is actually getting the 12V through the connector. Best I could do was clean connector pins, swish harness side of connector in, brush it and rinse with, 100% isopropyl alcohol, plug and un-plug connector while moistening with same alcohol to rub off any oxidation, and tightened the brass contacts. Finally, I coated with silicone dielectric grease and reconnected. Then, I went ton 18-mile drive and not a single occurrence. A couple of days earlier, I'd see the problem so many times during similar drive.


ALT CONNECTOR WITH DIELECTRIC SILICONE GREASE AFTER CLEANING AND TIGHTENING THE FEMALE CONTACTS


ALT CONNECTOR, HARNESS SIDE WITH PIN-OUTS

Toyota pioneered kaizen and eliminating waste. I am a believer of those so I gave Toyota a does of its own medicine - LOL!
In the process of checking my alternator wiring, that bulky "intermediate" alt connector caught my obsessive waste/bulk eliminating attention.
The intermediate connector for alternator is pointless.
Why the heck is it there, when 18 inches down the loom there is the main alt connector? (Maybe it made sense from manufacturing Point Of View but not to owner's POV.) It also adds bulk and more parts to break.
Further more, see that black ground wire that runs through the "Intermediate" connector then to the power steering pump bracket? It is NOT a part of the charging system! It is ground wire for the ignitor noise filter. It does not need to run back to the charging system connector then to the power steering pump mount bracket?
I snipped the intermediate connector off, securely twisted mating wires and soldered well, heat-shrunk and cleaned up wiring harness.
I did same to noise filter ground wire so now it physically goes directly to power steering pump bracket.
Now there's one less part to break, the wiring is cleaner, and my truck is a few ounces lighter! LOL!




BLACK WIRE TO POWER STEERING PUMP BRACKET IS GROUND WIRE FOR IGNITOR NOISE FILTER, NOT PART OF CHARGING SYSTEM WIRING.


GROUND WIRE FOR IGNITOR NOISE FILTER, NOT PART OF CHARGING SYSTEM WIRING, YET RUNS A CIRCUITOUS PATH THROUGH CHARGING SYSTEM CONNECTOR AND EVENTUALLY TO POWER STEERING PUMP BRACKET

Hey folks! I acquired an ‘87 4Runner a few months ago, and I’ve been googling how to repair some of the issues it has. Here recently, it wouldn’t crank. The battery was at or juuuuust below 12VDC, and nothing would happen when I turned the key. I jumped it, and I was reading 12.5 at the battery and 13.8 at the post on the alternator. The alternator harness (from the alternator to the plug at the passenger fender) ohm’d out fine. No opens or shorts. I decided that while the alt wasn’t at prime operating condition, it “should” be giving me enough to charge the battery - so I ran the “big 3”. Overkilled it, really: 0/1 from the alternator to +batt, with a 150amp fuse in hopes of an alternator upgrade in the future. 0/1 from -batt to a bus bar, with the same gauge wire going from -batt to the block, frame and passenger fender. Added 0/1 from the driver’s side of the block to the frame and 6awg from the head to the firewall. Cranked her up and I was reading 13.8VDC at the battery, and at the alternator post. She drove like a champ for about 10 miles and started to die out on me. First indication of it was the rear window going up slowww after my kid grabbed his football gear out of the cargo space. I killed the A/C & headlights and got back to the house. Pulled out the meter and read just above 12VDC at the battery and alternator. Turned her off and tried to crank her up again. The starter got it to turn over about twice and then nothing.

As far as the new wiring I installed, I’d read up a lot about this modification. I watched many YouTube videos, and all of them advised to reinstall the factory charge wire onto the alternator as well as the new fat wire, as well as hooking the fusible link to +batt, so naturally I heeded that advice.

I pulled the fuse box cover and noticed that the 80amp fuse element is now black. I distinctly remember that it wasn’t in this shape earlier this morning, before I ran this mod. I’ve since swapped out the fuse and the alt is now in the shop being rebuilt. While the fuse was out, I ohm’d out the fusible link that connects to the positive batt post and it’s good.

With the alternator out, I’ve taken some voltage reading with the key switched “on”, and with 12.61VDC, I had 12.49 @ B, 12.55 @ S, 12.34 @ IG & 11.83 @ L.

With this being the stock alternator, I can’t imagine this mod would be the reason that fuse is blown - but I’ve been wrong more than right. The shop said the alt was toast, and I’m trying to find out if there was any reason that it fried other than it just being old.

Also took some more readings while the batt was installed, alt removed & the key switched “on”…

11.92 @ both sides of the 75amp fuse
.003 @ both sides of the 10amp fuses
12.57 @ both sides of the 15amp fuse

Any help is greatly appreciated!

Please clarify exactly what is (are) the problem(s) now.
Cranking, firing and dying?
Blown 80-Amp fusible link?

The best upgrade is inspecting, cleaning and tightening all connections. Have you done that?
There is really no need to upgrade wiring, especially with today's energy efficient lights and accessories.

Cranked and combusted, or cranked, combusted and died?
"Turn over" is ambiguous.
"Crank" is starter motor turning (hence, cold-cranking amps rating on battery)
"Combusted" is air-fuel mixture igniting and engine runs.

Sorry, hard to visualize words. Mind showing it on schematic like I have above?
IF you added a thicker wire directly between battery and alternator AND LEFT stock "B" wire in, you are bypassing and defeating the fuse/fusible link network. Unsafe.

With good connections and no load (no alternator), B and S should be same because S is simply spliced to B near the battery.

Which fuses are those? I don't remember any 10-amp fuse in charging system. How do those differ to fuses you mentioned above?

First, and foremost, I want to thank you for your reply, sir! I'm honestly very thankful, and I want to ensure that my gratitude is not lost in the sauce.

At the time of the original problem, my alternator had quit. The 4runner started bogging down, so I killed any accessory running (lights, A/C, etc) and made it home. I grabbed my meter, and read just below 12VDC on both the battery posts & the alternator charge post. I turned the vehicle off, and as I suspected would happen, the started engaged and gave me a couple of revolutions and then stopped without starting the motor. Tried to crank it again immediately, and all I ever heard was a relay click near the passenger kick plate/glove box area. I then checked the resistance between the alternator post and case and it was shorted out. Verified this by taking it to a local shop, where they bench checked it. The 80-amp fuse was burned, but not open. I removed it and ohm checked it, and it checked out fine. I replaced it nonetheless.

I have installed all new grounds. 0/1 welding wire from the negative battery post to a the passenger fender (stripped paint to make contact with bare metal), to the front passenger side of the block, and to the frame - all by way of a bus bar. Added a ground wire connecting the frame to the driver's side of the block. Replaced the head-to-firewall ground, again, stripping paint from the firewall before installation, and used 4awg welding wire. Also, upon installing a rebuilt alternator, I added a ground between the bottom mount bolt and the frame, using 4awg welding wire.

Installed wire connecting the positive battery post to the alternator post, using 0/1 welding wire. The connection is made along with the original wiring. Near the battery, I've installed a 150-amp fuse. Also replaced the starter wire with 0/1.

All contact surfaces were wire brushed & cleaned at the time of installation. Also verified continuity of all new wiring prior to, and after install


I would love to post that schematic, but I haven't been able to figure out the URL thing. My apologies, as I understand that I'm making it hard to effectively communicate. I did in fact install a wire between the alternator and battery but wanted to leave the stock B wire in place, being that it has fusible links in place to protect the fuse box, as the new wiring has no connection to the fuse box that isn't protected by fusible links. If there were a surge, the link should melt, thus cutting power off to the fuse box, no? If that happens, wouldn't that effectively shut the vehicle down?



There was roughly a differential of .06VDC between the B & S connections. I chalked that up to my multimeter being old and abused.



My fuse box doesn't have a diagram on the lid, but by trial & error I determined that those 10-amp fuses are for the headlights. With them on, I was able to read over 12VDC, but I can't recall exactly as it was a few days ago that I discovered this.


There's an update on the matter. After installing the alternator last night, I read 14.02VDC coming from the B post of the alternator, as well as at the battery posts. All charging fuses checked very close to the same voltage. I took her out for a drive, and she died on me at a stop, about 1.5 miles from the house.

Pulling up to a stop sign, the engine shut off. All gauge lighting cut out. Turned the key back to "off". Turned it to "accessory" and my radio would power up, the cigarette lighter would get power. Turned the key to "run", and it all powered down. Turned the key to "start" and Nothing at all happened. No clicks. Starter did not engage.

Since I had some time (waiting on my kid to show up with the truck & tow straps), I checked voltage at the battery posts, and had 13VDC. I had no voltage at any charging system fuse. I believe that the fusible link between the battery post and the 80-amp fuse melted, because every fuse in the fuse box was in tact. No visual damage at all. All of the fuses above the driver's kick panel were good visually as well. I do understand that they should be tested with a meter, but it was late, my kid showed up to pull me home, and There was traffic to deal with. I have this unshakeable fear that someone will hit the vehicle while I'm working on it.

I plan on removing the link to test it this evening when I get home.

Also, a hokey thing was happening after the stop sign death: With the 4-way flashers on, they'd cut out when I'd open either of the doors, and the door lights would illuminate. On the tow home, when brakes were applied, the 4-ways would cease to work. On top of that, they wouldn't always work with the same switchology.

By the time I got it backed into the driveway, I was tired, fed up & needed a beer, so i decided to give it a look when I get home from work today. In thinking about it, I'm wondering if the ignition switch may be malfunctioning. Before I explore that possibility, I need to look at what I've been working on and see what all may have been affected by it.

Alright, I got to piddlin on the 4Runner as soon as I got home. Voltage readings at the fuses in the engine bay were non existent no matter the switch position, so I started checking for continuity via resistance.

Alt post to case: 89.6 ohm
Alt case to ground: 0.1 ohm
Charge (B) wire to ground: 3.2 ohm (short)
Fusible link to ground: 3.3 ohm (short)
Charge wire to FL: 0.3 ohm (short)
All fuses in box: 0.3 ohm (short)

In light of these readings, I decided to get a closer look at the loom coming from the driver’s fender to the fuse box. All of the wiring looked like it was in good shape.

I pulled the 30 & 40-amp fuses and narrowed the ground to the left pin (as seen while looking at the fuse box from the front of the vehicle) of the 40-amp fuse. This wire splits into two and is connected to a cannon plug at the driver’s side between the fender & air box, directly behind the headlamp. The other shorts were eliminated with the 30 & 40-amp fuses pulled.

I checked for ground at both terminals for these wires, and I read 7.0 ohms at the top right terminal, as seen while looking directly at the male plug terminals.

By then it was getting dark and I had to pack up for the evening.

Does anyone know where this particular section of wire goes to? It appears to be going to the marker & turn signal.

Attached Images

   

May I suggest you go to my thread on Yotatech? My photos disappeared on thie thread and T4R does not allow simple and direct attachment of photos. Complicates things because one has to upload to photo host, and take URL from that to insert into the T4R posts). Thread is here: How Charging System Works - 22RE - YotaTech Forums

Please disconnect the B wire from the Alt stud terminal and measure resistance from stud terminal to ground. Should be high. If as low as 89.6 ohm, you most likely have a bad rectifier on alternator.

That must be the "S" wire. It's spliced to thick white "B" wire near fuseblock. the other end goes to the alt connector.
Pin-outs for the round connector aka intermediate connector is on my Yotatech thread.