1981 300d alternator failing?
 

Hey guys and girls, I think I need a new alternator, but please tell me if I'm missing something here:

About 3 months ago, my daily driver displayed a glowing battery light. With a multimeter, I found 12-12.5V at the battery with engine running to confirm I wasn't charging. I removed the voltage regulator and found the brushes right at the wear limits. I replaced the regulator, charging voltage after repairs at 13.8.

Last week, same symptoms recurred: battery light and not charging. I removed, inspected, cleaned and reinstalled the voltage regulator and now have 14.7 volts. Car starts reliably and battery light has stayed off. I thought my problem was fixed, but I'm now having wierd symptoms:

-headlights are flickering from ~50% brightness to 100+% brightness with engine ~1000-2000rpm. Headlight brightness more stable above/below this rpm range. Radio backlight/display with same flickering symptoms.

-turn signals are working, BUT blinking very non-rhythmically...instead of a predictable "tick tock tick tock tick tock", they're more like "ticktock tick tock tick tocktick".

Confirm I need an alternator?

Thank you!
Brad

Try the below:
Set your meter to Volts AC and you should have a reading of ~100mVAC.
If the VAC is too high, then look for a rectifying diode failure.

Id be cleaning the negative connection at the fender well. Sounds like a classic poor ground. Check both ends of your cable too. I just changed mine which looked good until the insulation was pulled back a bit.

I went home to check voltage 1 more time and now have 17+.

I will check the VAC as recommended, but now I'm leaning back towards a failed regulator.

Yowza, 17+...hope my battery isn't cooked.

High DC voltages are usually due to failed rectifier diodes. As Diesel911 suggested, check for AC volts at the battery. If you have a failed rectifier diode, you will likely burn up another regulator.

Check your meter for accuracy also. A rough check is a new AA Alkaline battery should measure around 1.57 volts

I agree
 

Replace the alternator.


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