Batt light does not come on during check

[SaxAndLiz]

I searched the threads here and didn't find an answer that fits.

The battery light/ charging indicator light (see pics) does not come with the key in the On position, with the engine off. This is the opposite of the problem most threads are about (batt indicator on while driving possibly indicating alternator malfunction).

I just changed out the worn out brushes on my alternator and put everything back together. One of them was so worn down it didn't need to be pressed in to get it seated onto the rotor slip ring. I had multiple indications the battery wasn't getting charged before undertaking this project.

The alternator is not working, but maybe it's a wiring issue, and this is why the battery light is not coming on before starting the engine?

What should my next step be? Thanks!

-Sax

 

[brillo_76]

Did you replace the bulb? The bulb s do occasionally burn out.

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[SlickmisterN]

What he said ^^^

 

[SaxAndLiz]

Hah! Fair point. I guess I was just really hoping for a way to make my two two problems be linked and resolved together - this and the alternator not working.

I usually pay attention to the dash lights when I start all my vehicles. It seemed mighty coincidental.

Thanks!

Did you replace the bulb? The bulb s do occasionally burn out.

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[brillo_76]

I can understand that. These are all over 20 years old now. So bulbs can go at anytime...

Just best to verify that bulb is all...

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[19963.4lsr5]

The bulb is part of the circuit.

If the bulb is bad it could very be your easy fix.


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[SaxAndLiz]

So the bulb being out could cause a proper charging system to not function?

The bulb is part of the circuit.

If the bulb is bad it could very be your easy fix.


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[19963.4lsr5]

So the bulb being out could cause a proper charging system to not function?

Yes check the bulb or just put a new one in. It’s step 1

My battery light is on at key on.


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[brillo_76]

If your indicator lite do no illuminate when the key is on before engine start. Then they need replaced or fixed. This is how you know the bulbs are not burnt and that system is functioning properly.

Will the system still charge? probably you just will not know if your system voltage is low. That lite triggers when the system voltage drops below a certain voltage.

 

[TheDurk]

Pull the three wire plug of the alt and ground Pin 1, the Yellow wire with green stripe. Do this with key on and engine off. If the light does not come on, you have a wire fault or the bulb is burnt. This is way easier than pulling the module to check the bulb.

I don't know for sure on our Toyotas, but it is common for alts to require the bulb to be good to provide a voltage to 'excite' the alt into producing voltage. A simple voltage test will clear that up.

 

[19963.4lsr5]

Pull the three wire plug of the alt and ground Pin 1, the Yellow wire with green stripe. Do this with key on and engine off. If the light does not come on, you have a wire fault or the bulb is burnt. This is way easier than pulling the module to check the bulb.

I don't know for sure on our Toyotas, but it is common for alts to require the bulb to be good to provide a voltage to 'excite' the alt into producing voltage. A simple voltage test will clear that up.

Yes, it is part of the circuit. If the bulb is open (bad) the charging system will not work.


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[brillo_76]

Yes, it is part of the circuit. If the bulb is open (bad) the charging system will not work.


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Good to know.

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[phattyduck]

So the bulb being out could cause a proper charging system to not function?

An incorrectly working alternator might do the same thing too.

-Charlie

 

[SaxAndLiz]

It was the voltage regulator!

It wasn't the bulb.

So the alternator was thoroughly bad - the brushes were worn down, the voltage regulator and rectifier were both bad. How do I know?

Brushes worn down - one brush didn't need to be pushed down for assembly. I replaced both. No battery light during check and 12.2 V at the posts with engine on.
Voltage regulator - replaced and the battery light came on during system check (very happy I didn't have to replace the dash bulb), but went off when the engine was on. Strangely voltage with the engine on was 12.2 V at the terminals.
Voltage rectifier - replaced and the charging voltage jumped to 14.4 V. Also, I was not able to successfully conduct any of the continuity tests mentioned in the Repair Manual on the new and old rectifiers.

If you are wondering, yes, I removed the alternator about five times to try out all the combinations.

It troubles me that the Batt light didn't come on at idle, even when I turned on the headlights, and the charging system wasn't working. I don't want to add "monthly check the charging voltage" to my very long list of preventive maintenance routine. Any thoughts?

-Sax
(with much gratitude to everybody who's already chimed in)

 

[19963.4lsr5]

It’s good to hear.

The volt reg controls the bulb so if bulb was good replace the VR.

I have a Hall effect current meter installed and mounted the display in the Large block off plate to the left of the steering wheel.

So, besides my cig lighter volt meter I also can watch Alt output….all the time.

I like knowing things……


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[SaxAndLiz]

Thanks! As the vehicles age, they need more monitoring as more systems can fail. Would you care to share a picture of your setup, or a link if you did a writeup? I think I ran across one a while back.

It’s good to hear.

The volt reg controls the bulb so if bulb was good replace the VR.

I have a Hall effect current meter installed and mounted the display in the Large block off plate to the left of the steering wheel.

So, besides my cig lighter volt meter I also can watch Alt output….all the time.

I like knowing things……


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[19963.4lsr5]

Thanks! As the vehicles age, they need more monitoring as more systems can fail. Would you care to share a picture of your setup, or a link if you did a writeup? I think I ran across one a while back.

Look in my thread for my 97 SR5 build and repair thread. I’ll look at my parts and install.


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[phattyduck]

Any thoughts?

Get a Denso remain (by Denso) and ignore it for the next 150-200k miles again...

-Charlie