How to Check Voltage at Alternator with voltmeter ?

Hi,
I have an 88 GTA 5.7 I have a low voltage condition, meaning the car runs at about 9 or 10 volts now, and is going down slowly. Started reading lower and
lower a few days ago. I think I must be running totally off the battery, although the battery tests currently at 11 volts ( even though the dash guage says 9 or 10). Soo, where do I touch hook up my voltmeter pos and neg pins to the alt to test it with the car running ? I have the 3 pin connector. There are 4 holes in the connector, but only 3 pins in it. The wires are red, yellow, and brown.
I'll prob take the alt out, to autozone to test it, eventually, but I'd like to test whatever I can myself first.
Thanks
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User132384 Spilled my beer when they jumped on the table and

IMO, taking it out and going to Austozone would be easier. <G>
While the engine is running, if you take a volt reading on the battery and it isn't around 12 to 13 volts, your alternator might be fried.
Good luck with it!
NOI
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start the car and remove the battery. if the car dies the alternator is shit.
-- i am the darkest creation of god

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SSIN
I think you and your buddy have been sitting on the firebird too long sucking down cold ones.;) Taking the battery off and starting the car will definitely fry the alternator.
Put all the lights on, start the car and put the meter on and it should stay around 14vdc. if you see it dropping then you have a charging problem.........

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Never been a valid test and tells you nothing of substantive value...not to mention you can easily wipe out the diodes in the unit.
Original poster: As noted by others, use a DVOM and if you don't get 13.5 or so volts from your meter, you likely do have some alternator problems.
I believe the correct way is to measure between the charging wire on the back of the alternator and the negative terminal of the battery, but usually as CBHVAC stated, if you put your terminals of the meter on the battery and go from there, you should be OK.
If it's bad, I suggest you get a GM rebuilt one if you don't rebuild your own (I do the latter).
Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...
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i've done it for many years and never killed an alternator yet.
ofcourse if you have a volt meter use it . but it's not the only way to tell
-- i am the darkest creation of god

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Good way to lunch the diodes even on a non C3 car by doing that.
As CBHVAC said, do it right, use a DVOM.
I paid $25 for my DVOM from Sears and I use it for everything from component checking to fixing my own appliances.
I used it an hour on my grandpa's 1975 Kenmore washing machine, verified everything electrically and found my problem in 5 minutes, and fixed it myself in 10 for $30 in parts.
Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...
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i have a digital volt meter. but i blew all the fuses in it trying to test the voltage on my stun gun. haven't bothered to get new fuses.been to busy
-- i am the darkest creation of god

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S.S.I.N. Spilled my beer when they jumped on the table and proclaimed

I hope you're kidding. A Stun Gun puts out several thousand volts at almost no current...but it still could fry a DVOM.
NOI
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If he really tried that, he blew more than the fuses... Last stun gun we bought, was pushing the 75K range..but...hell...whats a Fluke from time to time? :)

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CBHvac Spilled my beer when they jumped on the table and proclaimed

We used to abuse Flukes, usually Fluke 77's. Never pused that type of voltage, hell, not even half that. I can't remember frying one though, but 75KV is definitely a hell of a long way outside it's limits. <G>
NOI
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Bigjfig Spilled my beer when they jumped on the table and proclaimed

I got one from Sears too, for $45. It even can test capacitors. In the last 4 years, I have fixed 3 printers, 4 VCRs, and 2 TVs with it, along with a lot of home wiring...
Well worth the $45, and then some... <G>
NOI
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Yea, this one is a digital AND analog meter. has a readout and a swing arm thingie (analog). It's good.
Sometimes when you see the swing arm jump, you know you have an intermittent connection (or you don't have the probe on the terminal :).
Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...
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S.S.I.N. wrote:

Um.. if you remove the battery while the car is running... the car will die nonetheless.
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OP here. I tested the voltage, with the car running, by touching the pos lead of the vmeter to the bolt on the back of the alt, that connected to the battery, and the neg lead to a ground, and got approx 11 volts on my analog meter. When I test the battery with the car off the reading is 11 volts. (Forgot to test the batt with the car running ).
Took the alt to Advance Auto and to Strauss Discout, both places tested it and showed the volts to be only around 1.9 !!
So looks like the 11 volts in my test was just the battery voltage.
Bought a new alt and am going to install soon.
Thanks
I the
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Thats the entire idea...your battery, with a good alternator, wont be just 12VDC...it will be higher, as long as the engines running.. the 11VDC reading was your first clue it was the alternator, and not the battery, as the alternator was not keeping up with demand of the system, and, as the systems designed to allow the vehicle to run off the battery in case of alternator failure, thats what it was doing...
If you didnt check with the engine running however, it was a waste of time.

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The alternator is tied into the battery via the positive lead and will supply a car the voltage it needs to continue to run. I don't know enough about the problems that may occur on a computer controlled vehicle if the pos. cable is removed from the battery while it is running so I'll leave that one to the experts. Nonetheless on a carbed car (without computer) removing the positive battery cable is a way to check the alternator that has been used for many years. I've done it myself on a few occasions.
As other posters have noted you can easily check the power output with a cheap Radio shack volt meter that reads DC volts. At rest the battery should have a minimum of 9 volts DC ( minimal amount to turn the motor over) and probably around 12 to 13 VDC max. While running you just put one lead on the pos. (red) and one on the neg. (black) cable. Anything above 13+ volts and the alternator is working. I remember 14.4 VDC from somewhere and that may be the number that you are looking for. When I check alternators I use a digital volt meter in conjunction with a Amprobe brand amperage meter that reads DC amps.
...Ron -- 68' RS Camaro 88' Formula Bird
http://www.frontiernet.net/~rscamero
Some are wise and some are otherwise
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RSCamaro Spilled my beer when they jumped on the table and proclaimed

On a non-computer carbed car it won't matter like you said. However, the battery acts like a capacitor, or a voltage regulator to keep voltage spikes off of the computer, and anything else sensitive...even if the battery is bad.
Big enough spike, your computer lets all it's smoke out... <G>
NOI
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wrote:

And with a Mopar product, if the battery goes south, even a little, give it up...under 11V and it wont run for shit.

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