79 with zero voltage from alterator?
Thread Starter
Racer
Joined: Mar 2005
Posts: 285
Likes: 0
From: Keller Texas
79 with zero voltage from alterator?
Autozone says alternator is good. Have tried 2. This is a 93 lt1 engine with stock 93 alterator in 79 corvette. I have no alt light but can tell the the car is not charging by the the low reading on voltmeter. I have been running this system for 8 years w/o problems. Volt meter on alternator with battery connect shows shows no volts while car is running. Car starts and runs but I can tell I am running on the battery. There is 11.5 volt while car is running on the battery wire and red wire. The so called white sence wire showing 11.2 volts.
Fusible link? Help
Thanks
Fusible link? Help
Thanks
Racer
Joined: Apr 2006
Posts: 340
Likes: 0
From: Warrensburg MO
11.2 is low. Alternator/voltage regulator is bad. I am assuming the voltage regulator is in the alternator. Suprised Autozone couldn't identify the problem, the machine they use is pretty accurate. Usually it will state what the voltage output is from the regulator. You might go back and double check this when they test it. Although it might say the alternator is good, double check the voltage regulator output on the tester.
TommyJ
TommyJ
Thread Starter
Racer
Joined: Mar 2005
Posts: 285
Likes: 0
From: Keller Texas
i dont think it is the alternator, i am seeing on a post from durango boy that the alt needs to read some resistance from the alt light in the dash to produce voltage, i dont have one and havent had one for eight years.
Instructor
Joined: Sep 2008
Posts: 222
Likes: 0
From: penngrove ca
I'm with tommyleea, regulator. Not sure, but most likely the reg. is internal.
You tried 2 alt. with same result? It's possible you got 2 bad alt. but, that seems unlikely.
I would double check the easy stuff 1st. Wire connections plug into. alt., tight belt. I went thru the same thing and the wire connection into alt. was not quite snug.
I don't know about 79 but on 76 there are fuse links that are under the brake MC that are fairly easy to spot.
Good luck
You tried 2 alt. with same result? It's possible you got 2 bad alt. but, that seems unlikely.
I would double check the easy stuff 1st. Wire connections plug into. alt., tight belt. I went thru the same thing and the wire connection into alt. was not quite snug.
I don't know about 79 but on 76 there are fuse links that are under the brake MC that are fairly easy to spot.
Good luck
Thread Starter
Racer
Joined: Mar 2005
Posts: 285
Likes: 0
From: Keller Texas
i am thinking its something that triggers the alternator to produce voltage. Everything else works-is there a fuse specific to the alter-that triggers it on. I think the regulator adjusts the volyage but something must turn it on?
Instructor
Joined: Aug 2003
Posts: 104
Likes: 0
From: Newfane NY
You are on the right track... a wire has an open, possibly from a fuseable link, corrosion or even mouse damage. 
The test at Autozone is with a complete wiring system like the one on the car.
I see this at the store I work at. (Not A Z)
Test show the alternator working, problem is with the car wiring.
Yes the regulator is in the alternator.
Check all the wires, fuseable links and fuses.
Battery voltage should always be at the large lug on the alternator, if not, trace the wire back and all the way to the source...
Good Luck
The test at Autozone is with a complete wiring system like the one on the car.
I see this at the store I work at. (Not A Z)
Test show the alternator working, problem is with the car wiring.
Yes the regulator is in the alternator.
Check all the wires, fuseable links and fuses.
Battery voltage should always be at the large lug on the alternator, if not, trace the wire back and all the way to the source...
Good Luck
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Thread Starter
Racer
Joined: Mar 2005
Posts: 285
Likes: 0
From: Keller Texas
I have recently installed a viper t56 trans so i have been all over the car specificlly under the master cylinder installing the hydraulics and by the starter. What the mystery is that all wires attached to the alternator do have the battery voltage-11.5. The alternator is putting out zero volts.
Racer
Joined: Feb 2003
Posts: 316
Likes: 1
From: The Woodlands TX
I know you said your 79 had no alternator light. I didn't think my 80 had one either till I had the cluster apart. Not sure about the previous years.
Reason being I said this is I had the exact same deal. Mine was as simple as a burned out bulb on the alternator light. It wasn't making resistance to tell the alternator to charge.
Reason being I said this is I had the exact same deal. Mine was as simple as a burned out bulb on the alternator light. It wasn't making resistance to tell the alternator to charge.
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
i just upgraded the alt in my 72. since i dont have a gen light in the dash i had to put a resistor in the switched wire to the alternator. supposedly when you have an alternator that came from a car that uses an alt light, you need that resistor inline to trigger the alternator to charge.
look up durango boys alt upgrade paper here, it talks more about the gen light and the need for a resistor
look up durango boys alt upgrade paper here, it talks more about the gen light and the need for a resistor
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
I have also seen a bad ground cause this. Double check all of your ground wires. Some cars have a ground that attaches to the plug wire brackets near the distributor.
I have also seen a situation on a 1981 vette where the bolt holding the fuse panel together on the firewall worked loose. This caused a bad connection, which did not allow the alternator to charge the battery.
I have also seen a situation on a 1981 vette where the bolt holding the fuse panel together on the firewall worked loose. This caused a bad connection, which did not allow the alternator to charge the battery.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
If the alternator is testing fine at Autozone, make sure you have voltage on the trigger wire going in to the alternator. If you don’t have voltage on this wire the alternator will not energize and charge. I’m kind of in a hurry tonight and I did not read all the post so I don’t know if you have tired this or not.
On the back of the alternator you have the large red wire, this is the charge wire. On the top you have two wires that plug in. I’m not sure of the color I don’t have a schematic on this here. On older cars the wire was black with a white stripe on the 79 it’s probably different. However, you should have 12 volts on one of these wires, if you don’t you may find this to be your problem.
Willcox Inc.
On the back of the alternator you have the large red wire, this is the charge wire. On the top you have two wires that plug in. I’m not sure of the color I don’t have a schematic on this here. On older cars the wire was black with a white stripe on the 79 it’s probably different. However, you should have 12 volts on one of these wires, if you don’t you may find this to be your problem.
Willcox Inc.
Burning Brakes
Joined: Oct 2001
Posts: 911
Likes: 5
From: TN
fusable link
I think you have burned the wire into at the fusable link in the wiring from the alternator to the horn relay. I am basing this on experience I had with my 70, I do not know the wiring of your Corvette. I am basing this on the wiring of my 70.
I put a rebuilt alt on my 70 and when I started my car I was looking at the amp meter, it pegged to the right and then centered. No more charging.The fusable link wire burned into just like it was designed to do and saved my wiring. I did not keep this alt.
I put a rebuilt alt on my 70 and when I started my car I was looking at the amp meter, it pegged to the right and then centered. No more charging.The fusable link wire burned into just like it was designed to do and saved my wiring. I did not keep this alt.
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
i had this happen to me, thurs. battery dead, battery light on dash was on, i checked all three wires coming into the alt. all had 12.3 volts,(after i charged the battery back).
with car running the voltage at the bat. terminal on back of the alt. was 3-6v, jumping around. pulled alt. and went to orielly auto., they checked it and said it showed good,
what the heck, yeah it was putting out voltage, but nowhere near enough, i bought a rebuilt 63amp one, installed it, checked the bat. terminal on the back while running and it showed 14.2 volts. fixed, and we noticed the volt meter inside on the console was showing just above 13volts, it has never read that high before since we've had it, you may have 2 bad rebuilt ones.!!! who knows?
with car running the voltage at the bat. terminal on back of the alt. was 3-6v, jumping around. pulled alt. and went to orielly auto., they checked it and said it showed good,
what the heck, yeah it was putting out voltage, but nowhere near enough, i bought a rebuilt 63amp one, installed it, checked the bat. terminal on the back while running and it showed 14.2 volts. fixed, and we noticed the volt meter inside on the console was showing just above 13volts, it has never read that high before since we've had it, you may have 2 bad rebuilt ones.!!! who knows?
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
the other two read what??? the red one on the connector should be reading about same as the stud at all times, engine running or not, key on or off....
now with engine/key off the other color into the reg should read zero volts, and with key ON engine running or NOT, should read about the same as the other red wires....
try revving the engine a good bit say 3000 rpm and see if that triggers the alt to start putting out.....if not, and the above desired conditions are met, you do in fact have good batter/system voltage on all 3 points, even IF it's lo....and you can't get it to charge, you got a bad alternator or POSSIBLE a bad wire connection in that plug to the regulator, and so the alt is not in fact getting voltage, when we think it is....
move them wires around a good bit with long nose pliars and monitor the ouput of the alt, engine running.....last chance saloon there....
Thread Starter
Racer
Joined: Mar 2005
Posts: 285
Likes: 0
From: Keller Texas
Correct, three wires with same voltage with car running-key on. Turn off and no volts on third wire. Voltage on fusable links on starter. Still alt not performing-zero. Electrically whole car works. It has got to be something with that signal wire. how can I mimic the signal to turn on the alt? Where actually does that signal wire originate?
Thanks
Thanks