Home page

Cool! NEW FEATURE! Add "Your Corvette Story" today

C3 Electrical

Ammeter is showing negative all the time. (1/24)
 5/12/13 2:35pm
eldredjamesLifetime Member
Lifetime Member
Send Private Message

Temple City, CA - USA

Vette(s):
1969 Daytona Yellow. 350 / Automatic.


Joined: 10/3/2010
Posts: 363

68 Silver Toy said: Can someone help me on this. My gauge on the car is telling me there is a discharge. Could it be a ground problem or alternator? When I put anything on like the heat fan or headlights on it shows discharge more. Thanks

My '69 is doing the same thing.  Always points to the left.  Am I running off the battery all the time?

Jim
Our Sponsors help support C3VR
Sponsor Ad

Re: Ammeter is showing negative all the time. (2/24)
 5/12/13 6:59pm
dyoes
Former Member

Send Private Message

Zachary, LA - USA

Vette(s):
1974 L-48 Auto. Just your basic Vette. GM crate motor w/vortec heads and intake. Crane cam. Scorpion rockers, Edelbrock carb. Lots of parts still in boxes... :(


Joined: 1/27/2013
Posts: 201

Does the meter return to zero (straight up) when you turn off the car and turn everything off?

______________


"Let them that don't want none have memories of not gettin' any."
- Brother Dave Gardner

Re: Ammeter is showing negative all the time. (3/24)
 5/12/13 10:52pm
eldredjamesLifetime Member
Lifetime Member
Send Private Message

Temple City, CA - USA

Vette(s):
1969 Daytona Yellow. 350 / Automatic.


Joined: 10/3/2010
Posts: 363

dyoes said: Does the meter return to zero (straight up) when you turn off the car and turn everything off?
Yes, it always returns to zero when I shut her down.


Re: Ammeter is showing negative all the time. (4/24)
 5/13/13 12:36am
rraider1
Former Member

Send Private Message

Woodland, WA - USA

Vette(s):
1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion


Joined: 10/14/2003
Posts: 1152

It seems to me it is indicating you are running on the battery which means your generator is not putting out (by it some wine)

Re: Ammeter is showing negative all the time. (5/24)
 5/13/13 7:32am
Adams' AppleLifetime Member
Lifetime Member
Moderator
Send Private Message

Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 19624

An amp gauge that shows a discharge all the time(while running) indicates the alternator is not putting out enough juice to carry the load. This could be because the alternator is bad, or not rated high enough amp-wise. It could also mean a bad/loose connection. I would first determine how much voltage is at the battery terminals while running, and compare that to the voltage at the alternator while running. If both readings are low(at or below 12v), I would suspect the alternator.

______________
Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Re: Ammeter is showing negative all the time. (6/24)
 5/13/13 9:31pm
dyoes
Former Member

Send Private Message

Zachary, LA - USA

Vette(s):
1974 L-48 Auto. Just your basic Vette. GM crate motor w/vortec heads and intake. Crane cam. Scorpion rockers, Edelbrock carb. Lots of parts still in boxes... :(


Joined: 1/27/2013
Posts: 201

The ammeter is essentially a voltmeter... Compares voltage at the starter connection and at the horn relay.  Higher voltage at the starter shows (+) amps, and vice versa.

Adam is right on.  What you can also do is connect your voltmeter at the battery with the car shut off (ignition on), note the voltage, then start the car and note the voltage again.  If the voltage goes up, it's charging and the ammeter may be bad.  If it doesn't change or drops a bit, you're not charging. 

In the "old days" people would start the car and disconnect the battery.  If the car died, it wasn't charging.  I was told that with modern cars (not that C3s are modern, mind you!) pulling the battery cable while the car is running could cause voltage regulator failure.  Anyone know if that's true?


______________


"Let them that don't want none have memories of not gettin' any."
- Brother Dave Gardner

Re: Ammeter is showing negative all the time. (7/24)
 5/13/13 10:30pm
eldredjamesLifetime Member
Lifetime Member
Send Private Message

Temple City, CA - USA

Vette(s):
1969 Daytona Yellow. 350 / Automatic.


Joined: 10/3/2010
Posts: 363

Looks like its more electrical work for me.  Thanks to all for confirming.  I went out to disconnect the battery earlier and thought I'd start the car but we ran out of juice before it kicked over.  I'll check out loose wires as soon as it cools off out there.

If I check the voltage at the battery, won't I always get the voltage in the battery?

Jim
Re: Ammeter is showing negative all the time. (8/24)
 5/13/13 10:36pm
eldredjamesLifetime Member
Lifetime Member
Send Private Message

Temple City, CA - USA

Vette(s):
1969 Daytona Yellow. 350 / Automatic.


Joined: 10/3/2010
Posts: 363

Please ring in on this.

If I need to replace the alternator, is there any problem with kicking it up from 63 amps to say 100 amps???
Re: Ammeter is showing negative all the time. (9/24)
 5/13/13 10:50pm
Adams' AppleLifetime Member
Lifetime Member
Moderator
Send Private Message

Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 19624

Checking the voltage AT the battery without it running will only tell you how much voltage the battery is storing at that time. What you are interested in is, is there  MORE than 12v there with it running? You should see at least 14v with the engine running, and no lights, or A/C, etc. on. Then check voltage AT the alternator, and see if there is MORE at the alt than there is at the battery. If there is, then you prolly have a bad connection somewhere. If the voltage is the same, your wiring is ok. Either way, if you do not see a minimum of 14v AT the alternator, engine running at around 1500 rpm, you have an alternator issue.

And...while it's true, we used to "test" alternators by  disconnecting the battery, it's not a good idea....it can definitely mess up a regulator, and/or the diode trio inside the alternator. Plus, that test doesn't really tell you how much the alternator is putting out....just that it is.
 It's best to use a volt meter. Thumbs Up


Oh...and no...if you want to up the ante with a higher amp alternator, there's no problem with that. 100 amp might be overkill, tho....


|UPDATED|5/13/2013 7:50:15 PM (AZT)|/UPDATED|


______________
Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Re: Ammeter is showing negative all the time. (10/24)
 5/16/13 7:06pm
eldredjamesLifetime Member
Lifetime Member
Send Private Message

Temple City, CA - USA

Vette(s):
1969 Daytona Yellow. 350 / Automatic.


Joined: 10/3/2010
Posts: 363

Here's the scoop.  12 volts at the battery with engine off.  13 volts while running and 14 volts at the alternator while running.  But the battery meter shows -30 amps and goes lower if I gun the engine.

I guess I'm in the market for an ammeter, as soon as I figure how to remove the old one and how to test it for sure.

Yes, I'm troubleshooting two problems at the same time, horn and ammeter.  Don't think they're related.

Jim