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I believe the OP is concerned why the light is on even though the voltages are normal

 

Light should always be on when not running. When not running or, charging there is voltage on one side on one side of the bulb, causing it to illuminate. After starting, the alternator excites and supplies voltage to the other side of the bulb effectively turning it off. If the light is still on while running, even dimly, there may be a problem. Checking charging involves more than just output voltage.. Need to check amp output and check for AC leakage, bad diodes etc. Be sure your battery connections are clean and tight. Load test the battery. Do not disconnect the battery while running as an alternator test method.

 

I'll go to Autozone and ask them to check charging system. Alternators have 6 diods(4?). If one of them is dead, alternator has 5/6 power but charging is still ok w/o defroster and blower on

 

Voltages are a little low, probably why dash light is on. Battery voltage just after turning off car should be in 13,6v range. Resting voltage is 12,6v after sitting for several hours. Voltage at battery should be closer to 15v with engine running. Does sound like one of the diodes is dead.

EDIT: just ran out to garage to measure. With engine running, I measured battery at 15v. Right after turning off engine, battery was 13,7v

 

You probably have a failing Alternator... give it some time and it probably will. Alternator voltage should be over 14 (14.4+ or so).

 

If I turn on high beams, AC, rear defroster and blower, which voltage should I see at idle?

 

Shouldn't drop voltage at all with everything on, still +14.5v at battery.
Once you've used battery to start engine, ALL power comes from alternator. Including the extra amount needed to recharge battery.

 

I got 3 used alternators. Advance auto checked 4 alternators (including my old one) and said all were fine.
Autozone tested 4 and said 2 of "new" ones were good.
Advance guy said noisy bearings, no noise in Autozone.
One of my "new" ones is reman., looking pretty new.
No more dim battery light!

 

Awesome work!

I've had better luck getting used OEM alternators from junkyard cars. Carry spare in trunk.

Also check battery-cables, measure resistance end-to-end. They can corrode under insulation and reduce power from alternator.

 

Thanks.
I don't trust their testing machines. I was driving my Jeep very far from my house and my alternator died. I could make it to closest Autozone, removed alternator and brought it in to test. They said, it was fine. I bought another one from them and installed it anyway, no more charging problem.

 

Is it possible for the battery/charge light to remain on and the alternator to be fine? I just bought a 2008 Corolla and it looks like the previous owner recently replaced the alternator and the battery (the battery has a date of 3/19 and is testing ok) but the charge light is still on. I bought 2 alternators from the junk yard (both OE Denso) and they both output 14.4V under idle, but i still get a solid charging light. I meticulously went through all the procedures in the Haynes manual and verified that the rest of the car is good.
Does anyone have this light on and has no charging issues? Is it common for these alternators to crap out after a while, or are they known to last the life of the car? It just seems unlikely that 2 random Denso alternators from the junk yard have the same problem.

 

I found some alternator diagram, but not from Toyota.
This is what can happen according to found diagram:
There are 3 diodes #3, sending voltage to rotor.
the voltage is applied to one side of battery light and there is ignition voltage on another side, no current going thru.
If one of the diodes fails to send voltage, 1/3 of time rotor wire works as ground for the light, so light is glowing with 1/3 of power (it is kind of like getting 4 volts instead of 12).
When your ignition is on, engine off, light is glowing 100%
Most of the time alternator can still work fine because regulator (not shown oin the diagram) tries to send more current thru rotor to compensate for dead diode.