Originally Posted by RAD4Runner

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:


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 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:




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

Originally Posted by Trek4fun

I have the exact same problem. 7 volts on one side of the charge fuse and 2 volts on the other. Did you figure out what the problem was?