How Charging System Works - 22RE
 

UPDATED WITH GOOGLE PHOTOS
(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:
https://cimg0.ibsrv.net/gimg/www.yot...6297b5b6e2.jpg

Close-up of alternator pin-outs is here:
https://cimg3.ibsrv.net/gimg/www.yot...df56cc29da.jpg

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 with regulator case @25°C (77°F)
Other Toyota alternator write-ups / manuals also specify 13.5 - 14.3V with regulator case @115°C (239°F)

WITH B-WIRE DISCONNECTED, measure resistance from screw terminal to ground. You should get Very High reading. I get 75 kOhms. That translates to 0.16milliamps draw from battery. If R is 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, regulator would think batt V is low and keep on increaing chargincharging V, which 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:
https://cimg6.ibsrv.net/gimg/www.yot...b83eeceec4.jpg



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

A question for 1990 vintage 22re, does the ecu have a hand in controlling alternator?

No. The regulator built into the alternator does it all. Why do you ask that?

Checking the Charge Light Circuit t Charge Light Fuse
 

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.

https://lh3.googleusercontent.com/vE...s=w954-h663-no
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.

https://lh3.googleusercontent.com/4I...=w1121-h663-no
NORMAL CHARGING CONDITION WHEN ENGINE IS RUNNING

Sticky this!!!

Video - Voltage Readings at Charge Fuse.
 

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.
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 eng1ne fuse.

Thanks for this.
 

Tearing my hair out on this intermittent no charge. Stumbled on this while chewing it all over and found this thread and fixed it. What was the problem? Here's a hint: the engine had been replaced.

I almost jumped the gun and threw an alternator at this, but the symptoms weren't right. So I pulled the alternator to have it tested at an electric shop, not a parts store, so I knew the alternator was good.

Here's another hint: I did a topside change because I could move the PS pump and not lose any fluid.

Awhile back, it didn't start so I threw a starter at it and didn't fix it, so after digging, I noticed the battery ground was on the frame - ie, insulated - side of the motor mount. Put it back where it was supposed to be.

Figure it out yet?

Well, I scanned through this thread and noticed that it mentioned a wire going from a plug to the PS mount bracket. Well, I just had that off and there was no wire on it. Yep. They put that ground on the wrong side of the motor mount as well.

It ran this way for a year or so, but finally gave up.

So, thanks. I don't have much hair to pull out, so this was awesome.

LOL!
Happy to help.
Yes, there should be battery negative to engine block ground. That's where starter gets ground for heavy cranking current. Earlier trucks did not have that. Starter got ground through collateral paths and that is unsafe/unpredictable.
May we know model-year-engine-transmission?

Funny... I got ONE intermittent charge and brake light fault last night. Now I need to look my own charging system over again.

1992, 22RE, MANual trans.

The story continues...

Went to start it later and no start. No bulb check, no gauges moving, no clicking. Checked around and found the 80 amp fuse blown. Found the main wire at the alt wore through the cover and grounded. Fixed it and still no start. Headlights work but don't dim in start position. I think the fuel pump runs, the key reminder buzzer works. I wonder if the short fried something before the fuse blew.

Oh no!
But ur nice description would help narrow down where to look.
This is not about the charging system anymore so please Search for Similar problem, especiallur same gen and 22RE or start a new thread, and we'll continue there.
Use "google" search above, not "post" or "thread".

Yeah, I need to start a new thread on it after searching. Just figured I'd update here.

I noticed a ground strap at the firewall by the back of the head. I wonder if they hooked that to a hose, LOL.

No need for a new thread. The connector on the main alternator lead had grounded to the case and blew the 80 amp fuse. Went and got a new fuse, put fuse in and still no start. Drove to lunch and as I was getting out of the car, I noticed a brand new 80 amp fuse on the seat.

Sure enough, I reinstalled the bad fuse.

Installed the new fuse and all is well at this point.

LOL! Early Christmas present.
Glad you got it working. Yes, many problems are caused by bad wiring.

Remember when I joked about the firewall ground being hooked to a hose? Well, it's hooked to a bolt on the valve cover. Is this correct? It seems to me that the valve cover gasket is electrically insulated from the head by the seals on the bolts and the main cover seal.

LOL re hose!
Upon quick glance, grounding comment^^^ sounds correct. I do not see any electrical part that may need ground through the valve cover so most likely that ground wire is to keep up the good practice of grounding every metal thing that is not supposed to have any voltage.

I can see that. But I also see a bolt holes on the head in perfect reach of the wire, so I dunno.

Valve cover is insulated from block by the gaskets and the rubber on bolt grommet, while the head is connected to the block by the head bolts.

So, i'm trouble shooting a no charging situation,

when i do the test above'


IGNITION ON/NOT RUNNING/ 7.5 amp fuse out, i get;
Battery Voltage 12.8
Negative side of charge fault light 12.5
Other side of 7.5 fuse slot 8.3v (should this be close to zero?)

Engine Running
Battery Voltage 12.5
Negative side of charge fault light 12.2
Other side of 7.5 fuse slot 8.1v (shouldn't this be the alternator output?)

Engine Running 7.5 fuse installed
Battery Voltage 12.44
back of fuse reads 11.1volts

problem happened on the road, but in proceeding weeks i was getting an intermittent battery charge light on...a few times.
but then it went away......
so when i got home, charged the battery ok/started the truck.
and tested the output of 1st alternator...failed.
'borrowed' 'new' alternator from my brothers truck/swapped it SAME PROBLEM.

BYI battery is less than a year old and charges ok with charger, starts and runs truck no issues...except not getting charge voltage.

First alternator tested at ACE Alternator shop in Yucca Valley yesterday said it was putting out too much voltage, like 19 volts, but they didn't load test it; Some reason/when a regulator is 'bad' they don't load test?
They also had a refurbed Denso ready to go, so got it/left my original one as core.
....not putting it on yet (that would be 3rd alternator in the mix), as i believe it's another issue/not alternator.

2nd one currently installed has same issue as first one, no output on alternator.
3-Prong Plug on back of alternator;
the IG/red wire exciter voltage is ok,
the large white lead has battery power,
The yellow indicator has the voltage from that 7.5 amp fuse.
i did hook up a jumper and grounded the yellow at alternator 3-prong plug. it successfully caused the battery warning light to illuminate in the combination meter
i even wired directly 12v from battery to exciter input to see if it made a difference.
fuses and links all good.....
unbolted fuse box so i could look underneath/All looks good.

still struggling with this today.....
any suggestions greatly appreciated...

should the battery warning light come on when one just turns the ignition prior to starting?
then once started the battery warning light goes off?

OH, AND THE BRAKE LIGHT IS ON REGARDLESS OF EMERGENCY BRAKE SWITCH POSITION...
i think i'm getting closer to the issue please help !!!

Hi PiTownPi,
LOVELY DETAILED REPORT! I wish everybody would do that.

Busy today and hard to reply via smartphone, but real quickly...
I don't know how low one side of the charge fuse should go in order to cause charge fault light to come on. I only have reading from my truck.
Yes, when u turn Ign on, charge light and brake light should come on. Off whn engine runs and alt starts to generate.
Toyota wired the brake error light to also come on with charge fault light. Maybe to get one's attention better.

With connector unplugged:
"S" wire always has batt voltage, correct?
"IG" has batt voltage when IGN ON?
"L" has same voltage from charge fuse?
Check that thin black wire that is grounded to on of the mounting brackets (P.S. or alt)? Sorry I have not traced exactly where the other end goes to.

U got a 22RE?

Will look more closely. I also had ONE instance of intermittent charge light on last week. As soon as I slowed down to pull over it went away and never came back. LOL!