Gonna need some help

[Ribbedroof]

Let me start by saying I'm no electrician.

For about the last 4-5 days that I've used the car, the battery (charge) lamp in the wagon has been VERY dimly lit while running.

My understanding of the lamp's operation is that if the alternator output and the battery voltage difference are outside the designed operational range, the lamp will illuminate.

I have checked all the connections, they are clean.

I checked the alternator output, it is 14.8 volts at the "bat" terminal

I have a remote start relay, voltage running is 14.8 where it meets the cable to the battery.

I checked the voltage across the battery while running/charging...14.8 volts

Battery voltage engine off 12.9 volts


In the daytime, you can't even see it, but overcast or dark outside, it is glowing dimly So far, no issues with starting, but really don't want to find out the hard way.

What am I missing?

 

[Wraith]

I'd check for a bad/dirty ground with instrument cluster if all that checked out already. Is the 14.8V at idle? I've usually seen that voltage at about 1800rpm or more.

 

[Ribbedroof]

Yes, that's at idle in park.

It almost goes out when RPM goes up (turnpike RPM)

No other symptoms of ground issues, but will look into that as well

I just hate to throw an alternator at it if that's not the issue, although the high voltage now makes me think that might be the case

 

[1evilregal]

check the voltage while it's running, and at different rpms... if the voltage varies at different speeds, the diodes are bad, but will still charge...

 

[oldsmobile joe]

My understanding of the lamp's operation is that if the alternator output and the battery voltage difference are outside the designed operational range, the lamp will illuminate.

you are correct, but the voltage that feeds the battery is not the same wire that feeds the battery light. since you have good charging voltage, the most likely cause is a faulty diode trio inside the alternator.
http://alternatorrebuildkits.com/the-diode-trio-revisited/
you can replace this your self with a rebuild kit or buy a reman alt.

 

[Ribbedroof]

Brown wire feeds lamp?

Kind of wondered about the trio after doing some reading, but...well see first line of first post 😆

 

[oldsmobile joe]

i use to run into this back when we use to rebuild alternators in the dealership. a very common complaint with an easy fix. most dvom's have a diode tester on them now. spec is .5 volts one way only.

 

[Ribbedroof]

Shocker....none of the chain stores have the diode trio in stock. Think I'll buy a reman and order a diode pack to fix this one, I have another dead one for the core.

 

[xitabl442]

I've had this exact same problem for over a year. I had my alt tested at the local NAPA and they said it was all good. Hmm.

 

[Local Hero]

I had the same problem on one of my A-Bodies. I swapped out the alternator with a known good used one I had and the problem went away.