I started my '79 Catalina this morning to go do a few errands, and the alternator light stayed on after starting. A quick revving of the engine would make it go away, and stay away. It wouldn't work, the battery's a year old and the alternator was pretty aged, so I drove to the parts store and bought a remanufactured one. I noticed putting the new alternator in there's an unused bolt threaded into the back of the alternator that's not connected to the battery stud. What's the purpose of that? The old one had it removed. I've helped my parents change them many times when I was a teenager, but I don't recall anything like that before.
I also noticed that alternator light will still stay on until I rev the engine, then it will go out. Is that a normal thing with old cars? The belt isn't slipping, and all connections seem good. I have a lifetime warranty, so I'll replace it if need be.
Unfortunately the quality of replacement parts these days is pretty lousy. (You went through that with your brake master cylinder!) Rebuilt parts are particularly a crap shoot.
The charge light should go out as soon as the engine starts up, if it doesn't there's a problem with the charging system.
You could consider installing a new Delco 10si "one wire" self-exciting alternator. This takes the charge light out of the picture though so you'd want to install an aftermarket voltmeter to monitor it.
At least with this alternator, it's 3 bolts and done, I don't need to take half the car apart, or bleed 4 wheels all over again. Haha. They really lost sight of practicality with today's crap. I pulled the thing out and put it back in 40 minutes. I'm wondering if the aftermarket stereo is causing an excessive draw. Whoever wired the thing in, didn't do it right. I'm pretty sure the speakers are all stock. The Fade, Balance, etc. All mess with the wrong speakers. I have the idle speed set right about good, I think. It's odd it would go out, then stay out, even after it returns to the same speed.
That alternator may have a hinky built-in voltage regulator. You could always try disconnecting the stereo if that's suspect.
I was thinking that. I'll unplug it either tonight or tomorrow and see if the issue goes away. I assume you can't put a better regulator in an alternator manually?
I forget how you change out the built-in regulator on those GM alternators. (It's easy on old Bosch alternators.) However since you just bought the thing I'd just bring it back.
Something squirrely is going on with the lights. The instrument cluster lights don't go back out when you push the plunger in, until the car gets shut off, then they go out. Headlights operate as expected. Starting the car, the battery light comes on, then revving the engine turns the panel on without touching the plunger. Haha. I'm not sure what caused this. I just noticed that battery light illuminates, even with the car off and the key out of the ignition if you turn on the panel lights with the plunger.
sounds like someone's been in there already
The dash dimmer doesn't work when the engine is running, but does when it's off. Something must have shorted.
Check grounds carefully. A lot of squirrely electrical gremlins are caused by bad grounds. The cable between engine and chassis is a common trouble area.
I'll check that. Pulling the alternator off may have disturbed it, like the brake line last year. That old alternator wasn't original, but the aluminum housing was pretty well corroded. My girlfriend's dad said he never changed it in the 10 years they had the car.
there's an unused bolt threaded into the back of the alternator
a particular model of alternator could be used in a variety of vehicles, so the bolt could be there for another application. Do you have a photo?
I also noticed that alternator light will still stay on until I rev the engine
The light means the voltage is dipping. (you can verify with multimeter or watch the headlights dim)
Maybe there's too much load (do you have aftermarket electronics?)
Or alternator doesn't produce enough power at idle. Does the engine idle normally? You could try downsizing the alternator pulley to make it spin faster. Get the alternator tested. Could be a dud.
You know, I actually didn't think about aftermarket stuff. Somebody at some point in time had completely wired in a subwoofer and all of that jazz. It's been taken out, but there is a line with a 100 Amp fuse that runs into the trunk, into nothing. All it has that I'm aware of is an aftermarket stereo with a CD player. Headlights do dim after revving, but not always.
I drove the car to work this evening, so I'll be able to watch the headlights on my way home tonight.
I had a similar issue with the light being on until I shifted to drive (along with crazy high voltages). It ended up being a bad regulator and everything went back to normal after it was replaced.
Could you please answer all the questions in the first paragraph? Starting out with what year it is? Thanks.
The relevant information is in my signature. You've answered many questions over the last 10 months about it, Doc. 1979 Catalina, unknown mileage. Over 100k.
You need to post this information each time you ask a question.
Here's the extra bolt in the back of the alternator. It's to the right side. I believe it's a 10 mm.
I vote on a new regulator. And you've been working on this Cat for a year and everyone should know you by now.
Check grounds carefully. A lot of squirrely electrical gremlins are caused by bad grounds. The cable between engine and chassis is a common trouble area.
I went out and jimmied basically all of the obvious grounds under the hood. Nothing was particularly loose or corroded. I pulled the top of the dashboard off and jimmied the headlight plunger connections and the connector to the cluster. The gremlins went away, and the alternator light no longer comes on, unless the motor isn't running. All is functioning normally. I'll drive the car to work again tonight and see if the headlights still brighten and dim with the throttle. Good thinking @chucktobais, credit to you for figuring this one out.
Sounds good! You might also want to check voltage at the battery with headlights and accessories running to verify alternator output.
Here's the extra bolt
Looks like additional grounding