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Hi
the volt meter in my 76 C3 isn’t reading, I have fitted a new volt gauge and this has not fixed the problem (the old one was faulty)
I have measured the voltage from the wiring and I get 0.6v when the ignition is on and 0.9 when the engine is running, can anyone point me in the right direction on how to solve this problem ?
That is an amp meter, not voltage and pretty much tells you nothing of the condition of the charging system. It is the only gauge I don't look at when driving. I have a volt meter I plug into my cigarette lighter when on a trip.
Ed
Definitely the original Ammeter. With the car running it shows if the system is charging (+ from the zero) or discharging (- from the zero)
The wiring for them is odd compared to a lot of stuff. It's a shunt circuit (sort of) so that the full current wasn't being sent through the gauge and it's not going to read correctly with a DVM or some other volt meter for testing as both of the wires going to it are actually positive. If you're trying to check the system use a different ground point and I believe the black wire with the stripe will show proper voltage
M
This is the meter I have I just assumed it was a volt meter with it saying battery ?
yep, as said ammeter.
also said, shows if alt is supplying current/ plus side or not supplying/minus side.
you get use to them as a general "idiot light" type gauge.
If your battery indicates -40 Volts (or even +40 Volts), you're going to have a bad day.
It can be replaced with a voltmeter, with a bit of wiring. Read the warning at Zip Corvette. Did you already try to run a voltmeter with out changing the wiring?
Hi
managed to check the wires tonight, I get 12 volts through one of the wires when earthed in a different location as you said
any recommendations on what to check next ?
DaveHarbinson
I suggest you do the following since you are asking for assistance:
With the KEY in the ON position, and the car OFF, take a picture of the gauge and post it. Also take a Voltage Reading at the battery terminals with a digital multimeter and take a picture of that reading and post that.
THEN
With the engine RUNNING take another picture of the gauge and post it (do not turn on any other loads). Also take a Voltage Reading at the battery terminals with a digital multimeter and take a picture of that reading and post that.
THEN
With the engine RUNNING (and turn on every load you can; lights, radio, fan, emergency flashers, etc.) take another picture of the gauge and post it. Also take a Voltage Reading at the battery terminals with a digital multimeter and take a picture of that reading and post that.
With those readings available the folks on this forum will have a better chance of giving you some valid feedback.
Originally Posted by DaveHarbinson
Hi
managed to check the wires tonight, I get 12 volts through one of the wires when earthed in a different location as you said
any recommendations on what to check next ?
3 things
1. Amp meter is doing nothing.
2. Car is over charging with no load, bad voltage regulator. Should not go over 14.5 volts.
3. Car is discharging with full load. Alternator not enough capacity to even hold battery voltage with load at idle.
You definitely have an issue with that amp meter. But you also have a serious problem with your alternator.
(hopefully these voltage readings were taken with a fully charged battery)
No need to apologise, we all needed to learn at one time.
The charging system on your new to you Corvette really isn't much different than any other car. The Amp meter isn't necessarily used much any more. And really isn't the most informative guage.
let's look at my old Corvette, a 77 model that has fuel injection and twin electric fans. These add ons use a considerable amount of current, messured in Amps.
when my car is idling, like yours I have power going to my distributor, coil and my dome light is on when taking these photos as the door is open. But consider that my electric fuel pump is running, (9 amps), and my injectors are also using some current. So, right off the bat I'm using more current just to idle.
So, my 6 year old AC delco battery, at rest, door is open so courtesy lights are on. Car not running and I did not freshly charge the battery, just the way it was when I went out to the garage.
As you can see, 12.4 volts. With the dome lights on and nothing else. A fully charged 12 volt battery should read 12.7 volts. Give or take .1 depending on temperature. The dome lights are likely pulling a tad.
Now let's start the engine and let it idle. Nothing on but those courtesy lights.
As you can see, at ldle, 800 RPM. voltage is at 14.4 volts. This is where my voltage regulator limits the voltage. This is perfect. If I rev the engine, the alternator output will climb with RPM. However the regulator will continue to regulate the voltage at no more than 14.4 volts.
Let's look at my volt gauge. YES volt guage.
Not quite as easy to read as a digital volt gauge. But you get the idea with it. Note everything over 14.5 volts is a RED zone!
Now let's crank up my stereo and turn on the High beam headlights.
At idle, high beams on, stereo cranking, 14.2 volts at 800 RPM.
Now for fun. Let's add on my twin electric fans! These really, really pull some power!
Now you can see at such low RPM with all these things going, I've dropped to 14.0 volts. A fully charged battery is 12.7V. So with my electric fuel pump, fuel injectors, High output HEI distributor, high beam headlights, stereo, twin electric fans and dome lights. I'm still throwing a charge at idle.
And at no time does the voltage go over 14.4 volts. Not even at 5,500 RPM.
This is how it should work.
your amp meter is doing nothing, but perhaps it was fried by your over charging alternator.
Your biggest issue is your Alternator. It's over charging with no load, and likely really overcharging when the RPM'S increase.
Your voltage regulator is inside your alternator. Unless you have a stock standard 68.
Fix your charging system first. Then go back to the amp meter issue. Or get a 77 volt gauge and put it in place of the useless amp meter, many have.
Not certain what you ordered Dave, hopefully the correct 3 wire alternator.
if you wish to learn more about how alternators work, the differences between them and correct wiring.
Please check out Mad electrical's Web site. Go to there tech pages. They do a fantastic job of explaining these things to the average guy. Definitely worth a read. (mad electrical.com)
Hi
new alternator fitted and this has now fixed the overcharging but the ammeter is still not moving, I will trace the wires back tomorrow to see if one has a fault and update you
Volt meter
