My daughter pointed out that the battery charging light was glowing very dimly with the engine idling. The battery voltage measured around 11.7V with the key in ignition position ll and with the engine running the battery voltage dropped to 11.4V. Furthermore in with the key in position ll only the oil light comes on and it goes out with the engine running. The car starts and drivers normally except that it revs up a bit before it settles down.
The lack of the battery light coming on during start like the oil light does makes me suspect the alternator brushes are worn out. The brushes are part of the regulator, which is separately and easily replaceable. Last time I bought one it was $35 US, probably closer to $50 US by now.
Mike
Good call... I've run into both the brushes issue and the braided ground line to the engine block being charging issues.
Bill
I re terminated the alternator output connections but I didn't check the brushes nor the grounding. I am somewhat puzzled that the alternator failure would cause the warning lights not to come on, except the oil light which comes on in position ll and goes out as it should when the engine is running.
That's what makes me suspect the brushes. It is a problem that I believe only exists in cars built in and around the '80s. The circuit seemed so serendipitous: the alternator lamp is essentially in series with the regulator's ignition input. When the ignition is on but the alternator is not charging, current flows through the lamp, the regulator and the brushes to energize the rotor and light the warning lamp. When the alternator is working, rectified output from the stator feeds the regulator, putting 12 volts on both sides of the warning lamp and extinguishing the lamp. Great, huh? But if the brushes wear out there is no path for current to flow through the lamp so it never warns you. The only hint (until the battery goes dead) is that the battery warning lamp doesn't light in position II.
Don't feel bad - it happened to our '85 765T and an '84 Nissan I had. I noticed the drop in the voltmeter in each, but wouldn't have noticed the warning light out in time. More modern alternators have regulators have a separate terminal for the warning light.
Mike
The design of the system requires current to be able to pass through the brushes (and the rotor) for the light to come on. So only stator, drive belt, and some regulator failures will turn the light on. All other failures, you're on your own, although the clue is the light not coming on before the engine is running.
Is the charge failure light burned out? That could cause these symptoms.
The bulb is ok. It was glowing very dimly. I turned out to be the alternator itself. Replacing brushes didn't cure it as the commutator was too worn out.
Regards,
Boris Mohar
Got Knock? - see: Viatrack Printed Circuit Designs (among other things)
void _-void-_ in the obvious place
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.