I have the nearly same problem with two of my rigs (an 83 and a 04 Taco). After starting them the charge light stays on for a couple minutes, it can be shortened to maybe 15 seconds on the Taco by revving up. Revving up the 83 seems to do little to hasten the light going out. This only happens after they have been not running for some time. If I start them daily it will not happen. When it occurs if I re-start several times in a row it will not happen. If I discharge the battery for several hours with the headlights on (up to 10 hours) and re-start it will not happen.

To restate this only happens after not running for several days.

The voltmeter in the 83 reads about 11.5V with the charge light on, then goes to 14V in about a second after the light goes out, after starting with no addition loads. I can turn on all the electrical loads it has including 420 watts of accessory lights (35amps @12V) and the voltmeter reads about 12V at idle (it has a slow discharge which is understandable). If I turn off the lights and other loads in about 3 to 4 seconds the voltage is 14ish. If you rev up to about 1500 with all those loads the voltage is about 13ish. With no loads at idle the voltage remains at 14ish. I've done all the tests in the FSM and other then the battery being a bit suspect as its 8-9 years old, the charging system is mint. I would think this is the battery but for the fact that the charge light should go out almost immediately even with a dead flat battery after boosting. The alternator has been recently rebuilt and tested (about 3 years ago, maybe 12000KM's put on) The described situation will occur of the truck has not run for about 7 to 10 days.

The situation with the Taco is nearly exact but will occur if it hasn't been started for 3 or 4 days. I've preformed all the FSM tests similar to what I did with the 83 and they indicate a tip top charging system. The exceptions are that you have to rev to about 2000 and the numbers recover quicker after prolonged discharge. In the summer I have an on board cooler which sometimes runs all day without the truck running and it did not exhibit this problem. The battery is about 3 years old and the alternator is an 7 to 8 year old rebuild (NAPA) with about 250000KM on it. The original lasted about 360000KM but the bearings started to squeal.

In both cases the problem seems to worsen the colder it gets. Several days recently were in the -15C to -20C range over night and both started fine but the light stayed on somewhat longer then described. When we had more seasonable weather last month it did as described. During the heat of summer which wasn't very hot, it would take somewhat less time than described. I don't think its temperature aggravated though. Yup kind of contradictory!

This morning the Taco did exactly as described with the charge light when I started it (currently its about -16C here) and I let it run about 2 or 3 minutes and shut it off, the light went off in about 1 minute without revving up. It ran at its 'cold idle speed' about 1200-1500RPM. I turned it off and let it sit with the headlights on for about an hour (it has auto shut off on the lights so I had to turn them back on a few times) and re-started it without any problems.

So the million dollar question...battery or alternator? The tests seem to indicate neither! I'm tossing the idea around it could be the alternator brushes are sticking and not making contact with the slip rings...but only after sitting for several days? Maybe the slip rings are getting slightly corroded not running, but the 83 would sit for months in a far more humid climate and this wouldn't happen.

The battery in the Taco is still warrantied as is the alternator (NAPA lifetime) so money isn't the issue...its freezing my fingers off in -15C getting the alternators out! The 83 likely should get a new battery, however I don't want to do the remove and replace diagnosis. I just know if I take the battery back (to CTC) they'll bock and say its the alternator and vise versa for NAPA.

Loose, dirty connections, etc., checked for and re-checked, and cleaned as required, drive belts newish and re-tightened.

It doesn't seem to get worse as time goes by...ie..3 months ago it light went off after 2 seconds and today it takes 60 seconds.

This started about 2 months ago for the Taco and about 6 for the 83.

I just re-started the Taco now and the charge light worked as it should!

 

Let's work on one truck a t a time. Take readings as described here and let us know:
https://www.yotatech.com/forums/f116.../#post52401963

 

O/K...83 first (11 Oct)

The wiring/troubleshooting steps that you described are different then that of an 83. These are the results I got following the 83FSM. Truck has 55amp 'cold climate' alternator and IC regulator

engine off voltage...12.6V
start engine, charge light on, 9.8V, engine runs about 10 seconds, charge light goes off, 14.3V after about 5 seconds
amp meter reads 37amps (on heavy white wire, maybe 10AWG) and goes down to 6.4 amps after about 5 - 6 minutes (engine warmed up @ 750 RPM) 14.3 to 14.4V the entire time
sped engine up to 2000RPM and reads 9.5amps @14.4 volts
turn engine off
Check voltage on yellow wire of regulator/alternator 12.1V, battery voltage 12.6V (I am assuming this is voltage drop across semi-conductor junction(s))

Checked charge light relay with a variable voltage source and it switches at 11.4V

Installed good (presumably, from a guy who did the GM alternator swap) used voltage regulator, started and got about the same voltage and current readings and no issue with the light

Restarted again with no problems with light, goes out immediately. Ran engine about 10 minutes to ensure battery was recharged

Tried it the next day without any issues. (12 Oct) Battery voltage 12.6V. Clamp on ammeter reads 36A and decreasing

This morning, started engine and light stayed on about 5 seconds (15 Oct) Battery voltage 12.6V before starting. Clamp on ammeter showed about 35A decreasing

 

There you go! That means a lot! That's why it's important to indicate model-year-engine-transmission-trim, etc.
Toyota Wars!

Schematic is here:



NORMAL charging voltage should range between 13.5 and 15.1 volts, dependent on temp and battery state of charge.

Sorry, just saw this part^^^ a 8-9 year old battery should no be a bit but should be the first suspect. One's lucky to have a good battery after 4 years.
"start engine, charge light on, 9.8V, engine runs about 10 seconds, charge light goes off, 14.3V after about 5 seconds" could be symptom of a bad battery. Have it tested first.

Other possible causes:
1) Bad wiring of IG wire. Check that IG always gets 12V.
2) Bad regulator, but you said you also had problem with the other regulator.
3) THEORETICALLY extremely high capacitance of the noise suppressing condenser, so IG starts low upon turning IG switch on then rises as condenser charges.

Then let us know.

 

Checked the wiring to the regulator/alternator. With the engine not running but ignition on as well as running I wiggled all the wiring, even under the dash and steering column, as well as jiggle the ignition cylinder/key with no change in how the light works. Battery voltage was there when it was suppose to be.

Started it hooked up to a battery charger/booster with no difference.

The capacitor as you implied would have to dramatically increase in capacitance, say from its 1-2 mfd to 25000 mfd + for that to happen. I disconnected it anyhow and tried, no difference.


I turned my attention to the Taco and found the slip rings on the alternator were badly grooved, beyond re-surfacing. A re-built alternator has fixed that. I guess when it would rev up it would re-seat the brushes giving a false induction by all FSM tests that it was working fine.

 

Yup, that's why I said, "THEORETICALLY" and "extremely high capacitance"

And what did you do about this^^^? Simple things first.

 

Hooked it up to a charger before starting for about 4 hours. Then put the charger on the boost setting to start the truck with no difference.

 

We're wasting our time here.
Eight-year old Battery is SUSPECT. How.difficult is it to have it tested?
Charging a battery is not the same as testing it.
Charging a bad battery for days does not make it a good battery.

 

Started truck (this is the 83) evening of 21st Oct...light stayed on for about 5-6 seconds.

Took battery from wife's 3 year old Corolla to try...light didn't go out for about 5 seconds. Put battery back in Corolla, started it (the corolla )and light went out immediately

Took battery to a heavy truck place in town on the 22nd. The guy there tested it and said its O/K, what exactly O/K is I don't know. I would think in a place were it can get to -35C, O/K means it'll start your vehicle at -35C . As best I could see the gauges over the guys shoulder both the ammeter and voltmeter were in the 'green' range. The ammeter looked like 450A and the voltmeter looked like 10.5V. after about 30 sec.

Put battery back in truck and started it without re-charging...the light went out immediately!

Swore at it...drove it around for about half an hour to fully re-charge battery.

Started it this morning...light came on for about 3-4 seconds. Re-started it 4 times in about 2 minutes and the light went out immediately each time. Wiggled all the wiring and connectors which could even remotely have anything to do with it and couldn't repeat the problem.

 

Solved...corroded wire crimp on the female spade connector inside the alternator wiring harness connector. Re-did all of them and a little dab of silicone no-corrode grease was applied

Thanks.

 

Many months later...

I wont turn over period. Battery is dead so I jump start it and go for a drive. Noticed voltmeter reading lower then normal but in the "acceptable" range. Stopped for gas...yeah you guessed battery dead! Got a boost and got home and turned it off, and it wont turn over. Put it on the charger for a day, still wont turn over, but starts if you jumper it. Turn it off...no turn over.

Put new battery in and problem solved.

Lesson learned...any time you have a this sort of electrical problem don't be cheap, just go and get a new battery especially if its more than 5 or so years old. Flippin' Scottish genes!