For the first time in the 6 years i've owned her she left me on the side of the road today. Maybe she's upset cuz she knows i'm trying to sell her.

Anyway, turns out my alternator is dead again. This is the third time I've replaced it which should probably be a hint there is a bigger problem. So, can y'all educate me on how Alternators die and where to look for the root of the problem?

Oh, and if anyone's looking for a 74 L48 "fixer-upper" send me a PM.

 

Stock Alternaotr with no big load items? Halogen Lights, electric fans, thimper stereo?
If its all stock, there are only a couple things it could be, Bad parts (diodes inside the alternator) and excess heat. Are the vents clear on the case? Dirt can gather up in there and cause the regulator and diode trio to overheat. Lots of remanufactured alternators die because of cheesy parts and poor workmanship. Theoretically they should last for years.
If you do have a bunch of high current stuff on the car you may simply be overloading the thing over time, for instance a 68 amp stock alternator run at 60 amps for a couple years might give up if it was buils less than perfectly.

 

What after market goodies have been installed that might be putting a strain on the alt?

Have you checked the condition of the battery lately?

 

i have a 100 amp powermaster alternator that suddenly and without pre-advice it's death, i have no heavy loads whatsoever to feed, no power windows, no ac, no heater (nearly no lights...)the engine runs pretty clean and fresh all the time, i've only got two big electric fans to keep the whole sistem cool...i went out one night, 1 hour cruising around and, after filling some gas, the battery was flat death...thanks god a crowd of youngsters arrived to push me, in exchange i had to show up a sweet burnout all round the city center

 

Yea, I have heard of a lot of Powermasters dieing.
Pretty much a crap shoot in buying a reman unit. I would just rebuild it myself, I figure I have a better chance of getting it right

 

I am 100% stock and was running with no lights, no radio etc. It was a brand new battery (i had just replaced it because the alternator ate the last one, although I didn't know for sure that was why it died, now I am pretty sure), and within a week (and maybe 150 miles max) the new battery was dead.

The only thing not stock on the car (and the only thing on the car that should require any juice) is the MSD 6A. Maybe I screwed up the wiring? But i installed that over 5 years ago if the wiring was really screwed up I think i would have other symptoms.

I am throwing out the bad alternator theory because it has been 3 alternators in 6 years and I assume when you say "should last years" you mean more than two.

 

Heat can do it.

AND:

Back when I had the TH400 and 3.70 gears, the alternator would go if I drove more than 40 or 50 miles on the highway. I had a lifetime replacement alternator, but it did get old replacing it over and over. I went to a larger pulley to slow it down and never had any trouble again. My logic was based on nothing more than "maybe it was turning too fast, generating too much internal heat, and melting the shellac on the windings." Couldn't tell you if it is science or luck.

 

OK, I say from bitter esperience.....

on other GM car of the past, some decades ago....the wiring is similar but the color codes are not....our vettes use very easy confused colors to the regulator assy/plug....IF that plug is reversed, for some reason the alt will function normally so it seems, for a while....dunno just why, just does....never seen a good schematic of the regulator to bother doping it out....

what does happen though is looking from the back of the alt, you have two terminals....they are supposed to be marked, but in fact over the years either the markings are removed in sand blasting/rebuilding, or never there to start with....

the most clockwise terminal...takes the typical RED wire on the new conncetor...and it at +12 all the time.....

the LEAST clockwise term is connected to the switched voltage/ignition, through either a resistor wire in cars without a idiot light, OR the idiot light....marked, Gen/Bat/Alt the terms vary a bit....

SO that means IF the key is on, engine still, the regulator in the alt goes to ground on that one terminal, and the light lights up.....

but typically upon starting, someone flashes the key so fast the alt maybe not able to go to ground long enough to cause internal failure....

leave the key on long enough with those two terminals reversed, and you got a bad alt/regulator.....the light bulb circuit wants to ground a hard 12 source....

but the thing will still more or less work...the key is....the lightbulb will glo dimly, seen most easy at night, obviously...

 

Gene, if the wires were reversed, the reference terminal (the one the idiot light is supposed to be connected to) would in fact get +12 (Battery Voltage) which will be higher than the ground side of the idiot light. Would that not drive the alternator output down? Also, with the idiot light side of the harness connected to the field side of the alternator the idiot light should be on all the time, right?

 

6', I have seen smaller more illegible schematics of the internals of a C3/SI series alt....there are reg differances depending on the specific alt output rating.....from what I HEAR it maybe have 3? sizes of outer cases/winding diameters....I do know the SI17 I have is about 1/2 inch larger in diameter? maybe an inch...than the stockish size on a '72 vette/'70 Goat convertible, or many other cars of the ear, even B body cruisers.....

when the key is on and engine running....IF the wires are reversed, the silly alt is looking at the above referanced #2 wire (most clockwise from rear view) through the lightbulb, or maybe a resistance wire as in some of our vettes.....so that lightbulb is taking essentially a switch 12 volt source into the main sense circuit, the power drain is very slight, and given up the secret by that bulb is very dimly lit, only seen at night....
ask me how I know this crap.....hard KNOCKS....damnit...

so the #1 wire as noted above...is offhanded connected to the allways hot 12 volts....but the reg is shut down by the other side being switched off....so it's neutral...METHINKS.....no one home, shut down....

so we get in the car, goose the carb, hit the switch, and start up....everyone goes HIGH.....except that silly light bulb glows dim....sense wire is wired backwards.....

I sat down some years ago and got to wondering about that damn stupid red dash light glowing like that, really dim....and tore apart the entire damn harness to find out just PERZACTLY what was WATT, and who wuz where.....

and proved my own wiring error, symptoms, redid it right, proved the cause/effect, and deliberately miswired it again.....proof positive....

I can say with the two termnals reversed you can get all sorts of charging/odd operational discrepencies rpm related, sort of like a 'one wire' marine alt in a car...differant animal...

in fact this chebby marine engine here now, I wired that alt so the thing runs like a CAR, in that it don't require high revs at cruise to actually charge the battery (x2)...thank you Perko.....

sorry to take up so much b/width for what is a simple problem, but to most guys it's NOT all that simple....but can cause mucho problemo as it did to ME, before I got the time and anger to figger it out....

 

Gotcha, BTW, the marine application is like that because the marine applications are run at WOT more than anything else.

 

heat, age and overload. The bearings and brushes wear out over time. Overload creates heat. Too much heat cooks the internal windings. Heat is the biggest enemy of anything electrical.

 

I am starting to wonder if my car is wrongly wired??

Yeaterday my car would not start. Ther was youst not enough power to drive the start engine. But when i disconected the wires on the alternator, and reconected them (in the same place) the engine started. (all the time there was enouugh power to let the lights glow 100%)
Why is this?
Whish bulp is it i shall check to see if te wiring is reversed.?

When driving. How much increase can you people see on your voltmeter. I youst barley see a difference. Youst abowe 0.
But i now the gauge is working, because i see a increase on -10 when ex using the eletrical windows.

 

What's a "idiot light" or a "silly light"?

I need to re-read those posts, but from what I got so far some wire being on the wrong side of the plug may make it seem to work correctly but really be frying inside and a dim "idiot light" is the only visible symptom. So, what's an idiot light, and does my 74 have one?

 

The idiot light is just the GEN light in the gauge bezel. That bulb is there to tell you if the system goes to ground. Also, that bulb and the IGN signal with it tell the alternator to charge.

If you disconnect that wire you will never see any output from the alt...it'll just spin.

 

There are a bunch of really OLDE TYME hotrod terms of 'endearment' for later model engineering....elimination of gauges for the unintelligent, mainly women...sorry chicks, but even most men don't unnersand electricals....no bother...just the way it is...

so the elimination of the true AMP meter from cars was done to favor a cheeper lightbulb AND since it glows RED, it tells the 'idiot' driver something is rong....red light, red traffic light, warning, no GO??

Even though sharks have a 'ampmeter' the thing is not wired to the same post on the alt, as the 'idiot' light....
meethiniks it was an attempt to 1/2 step the demand for actual instrumentatioin and the fact of the alternators used being generic to the rest of the line....so they used a resistor wire in most C3/sharks in place of the lightbulb...

the wiring changes among applications in these years, depending on market demands....model of car....SALES....and trying to adapt to saving MONEY....lends to our tech confusion....