BKbroiler

I've had this same issue with 3 different alternators in my 77. The current one is a new AC Delco unit. The problem is, with headlights on, the volt gage will move back and forth from 13v to the red area then back again. As it moves, the headlights and dash lights change brightness, kind of flickering. Same thing with high beams on. Gage moves with headlights off too, but not so extremely. Nothing else is affected, ignition is good, charging is good.
Any idea what's going on?

corvetero

Then maybe the problem is not on your Alt. but the headlight electrical conection

cardo0

I'm sure u have a hand held voltmeter and can read it for voltage. Since the batt is right next to u hook up your hand held to the batt terminals and drive the car as u compare the hand held to the installed voltmeter. If they don't track together the installed meter is bad or not connected correctly. If they both track then the charging system is disfunctional or something is loading it like a loose short or ground.

Good luck.

Richard454

If the headlights are getting brighter- the voltage is indeed going up...the flickering might be AC being introduced as it sound like the alternator is toast..

Get you meter- turn it on AC -yes AC and turn on the headlights w/ the car running- if it's showing more than a few thousands of a volt AC- then the diodes are shot.

Richard

The13Bats

It would be hard for me to believe 3 alt all have the very same issue so yeah likely some place else, headlights on, big load, but start with what cardo0 said place a volt meter at the battery see if it mimics the dash gauge, if it does which I think it will then you have a loose connection or even a low level short, check all the connections I had a ground lead on my trike causing a hard starting problem that wasn't easy to at fist check tell was loose.

BKbroiler

Thanks for the responses guys. The problem has been consistent with 3 different alternators. I do have a meter. Need to start checking.

The13Bats

I believe it will be a connection somewhere...just an early shot at it....

jnb5101

Do you have the correct size pulley on the alternator? Too large a pulley will reduce the output at idle.

The13Bats

also do you tap off the alt hot lead to power stuff....

BKbroiler

All pulleys are stock size and no extra stuff being powered off the alternator. Need to check a few things with the meter as suggested, but keep thinking. Thanks.

The13Bats

the fact it's not a steady needle but jumps about tells me things about what is might be or might not be....will wait for your volt meter test.