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In my 64, the ammeter gauge does not seem to move from the center. I tested the meter by applying a voltage between both terminals. That seems to work fine although with 5V the needle only moves about 1/3 of total gauge scale to one or the other side. Is this ok?
The feed wires themselves (black and black/white) both measure about 11.7V when engine is off. When I start the engine, one end reads 13.7V, the other 13.3V. That tiny differential is definitely not enough to move out the ammeter (given that the 5V only move 1/3rd of the scale).
So my question: is there a problem or not?
I only count on the ammeter as a gross indication of charging health. I will also say that if you didn't connect any aftermarket accessories properly (Vintage Air A/C; headlight relays) that the 'remote sensing' aspect of the voltage regulator can cause the alternator to not supply the full current required and hence, the ammeter misreading. I connect major electrical accessories to the horn buss under the horn relay...
You can read more about the issue on the Mad Electric technical part of their web site...
The C2 ammeter (unlike C1 full flow ammeters) operate off a shunt...it takes VERY little to move the needle based on that.
Last edited by Frankie the Fink; 01-26-2017 at 10:51 AM.
In my 64, the ammeter gauge does not seem to move from the center. I tested the meter by applying a voltage between both terminals. That seems to work fine although with 5V the needle only moves about 1/3 of total gauge scale to one or the other side. Is this ok?
The feed wires themselves (black and black/white) both measure about 11.7V when engine is off. When I start the engine, one end reads 13.7V, the other 13.3V. That tiny differential is definitely not enough to move out the ammeter (given that the 5V only move 1/3rd of the scale).
So my question: is there a problem or not?
I can't answer your question directly... but let me relate a story that applies to my 63. I'm not an electrical engineer. I'm just a hobbyist who has fooled with cars for 50+ years.
About 8-10 years ago, I noticed that my ammeter wasn't moving much, even if I cranked the car a lot to get it started, it never moved much above the "0" mark. It moved a tweak, but that was it.
That is not the way I remembered it working in years/decades past.
SO.. I removed it, and sent it to a fellow to check it out. He tested it and sent it back, stating it was OK and functioning normally.
Fast forward to several months ago. My speedometer quit and I had to pull the entire cluster. Sent it to a friend back in Maryland to be rebuilt. I mentioned the ammeter "issue" to him.
When it was done, he called me back. Told me he had fixed the speedo/odometer, rebuilt the tach too.
Also told me that he replaced the ammeter "guts" as the one in my car was an old reproduction. He put used original "guts" onto my existing face.
Now, my ammeter "swings" like it used to, and I'm a happy camper.
I've owned this car for 50 years, and the cluster had been out several times in years past. Somewhere along the line, that ammeter was replaced with a repro.. I don't remember when.
Be advised that an ammeter measures amperage, not voltage. You need to check an ammeter with your DVOM set to 'AMPS', not 'VOLTS', if it is in fact a real ammeter and not a voltage gauge.
Be advised that an ammeter measures amperage, not voltage. You need to check an ammeter with your DVOM set to 'AMPS', not 'VOLTS', if it is in fact a real ammeter and not a voltage gauge.
Be advised that an ammeter measures amperage, not voltage. You need to check an ammeter with your DVOM set to 'AMPS', not 'VOLTS', if it is in fact a real ammeter and not a voltage gauge.
The C2 ammeter gage actually measures the voltage drop across a approx 6 foot section of 10 gage electrical wiring (red) in the engine compartment.
A 64 (and all C2's) do not have an ammeter, they have a "battery" gauge. It measures a drop in voltage across the wire going from the starter 12v to the horn relay 12v. It takes a very small voltage to move the needle. If your battery is fully charged, you will see very little movement in the needle. With the engine not running, if you turn on the headlights, you should see a small jump to the left, usually about 1/3 of that half of the scale. It will probably drift back toward zero after the initial surge. If turning on the headlights doesn't cause a move to the left, you may have a bad connection at the horn relay, starter, or in the bulkhead connector. That wire is not one that is used to carry current for any other function. It's sole purpose is to have the small internal resistance of the wire drop a voltage, either + or - depending on which end of the wire has a higher voltage. They will read almost identical with a voltmeter.
If the battery is low, when you start the car, the needle should move to the right and then back toward zero as the battery charges and the voltage stabilizes. They are not accurate and the +30 and -30 do not reflect actual 30 amp draws or charges. It is meant to display a charging system health as to charge or discharge. A large percentage of the time the needle will be very close to zero.
If it is not deflecting, the first thing I'd check is the connections in the bulkhead connector that the black and black/white wires pass through. It takes very little corrosion at that small a voltage differential to cause no deflection.
PS As said, a 1.5v battery (flashlight, toy, etc) when connected with the negative to one terminal on the battery gauge and the positive to the other connection will cause a full scale deflection. Don't leave it connected, just touch momentarily.
This is the wire that the voltage drop is measured on. The black wire on one end of it, and the black/white on the other end of it pass through the bulkhead connector and directly to the two terminals of the battery gauge. That is it's only function.
Well, as I wrote even 5Volts only causes 1/3 deflection, so indeed this indicates a faulty ammeter...
Just to verify, you connected the battery across the gauge and not from one side to ground? If you try again, I wouldn't use a 5v battery, I'd use an AA or AAA 1.5v. If you peg that needle to hard, it can stick or slip on the shaft.
Failing battery gauges are not very common and when they do fail, it's usually an open winding, no deflection at all. There's very little to fail that will cause partial deflection.
Just to verify, you connected the battery across the gauge and not from one side to ground? If you try again, I wouldn't use a 5v battery, I'd use an AA or AAA 1.5v. If you peg that needle to hard, it can stick or slip on the shaft.
Failing battery gauges are not very common and when they do fail, it's usually an open winding, no deflection at all. There's very little to fail that will cause partial deflection.
I started with a 1.5V battery, but because that gave so little (barely visible) I cranked up to 5V....
It's strange because it's not much more than a magnet and a coil. As you said little can go wrong.
I'll take the jump and buy a new one and then wait for the moment I find the courage to take the cluster out
Looking at the wiring diagram for '64 corvette you can see the the ammeters 2 wires are connected to each end of the red wire between starter solenoid and the positive junction stud on the horn relay. Yes the "ammeter" uses that red wire as a calibrated shunt to measure current flow and polarity as a voltage drop across that red wire. Many will try and call that meter a voltmeter because it does sense voltage but the entire meter and shut (red wire) are calibrated to represent current flow and polarity - not voltage.
If you trace out the ammeter's wires you find the black wire is connected to the starter solenoid at the battery cable junction. The black and white wire is connected to the positive junction stud on the horn relay. While the red wire is a dead short between them. For example when the engine is off and you turn the key to start which way is current gonna flow? Yes from the batt cable post on the solenoid to all the loads on the pos junction post on the horn relay. Once engine running which way current gonna flow? Yes from generator (alternator) connection on horn relay back to that batt. Take it or leave it that's how it is.
Now the problem occurs when any of those wires - ammeter or red direct short - are changed with some wire of different resistance. Changes in wire diameter or length will change their resistance also and now you have a uncalibrated ammeter gauge. How to fix this? If you don't have original replacement wire then you are in for a whole lot'a experimenting and testing. What I'm saying is the problem can be the wrong wiring just as easy as a bad ammeter gauge.
Looking at the wiring diagram for '64 corvette you can see the the ammeters 2 wires .........How to fix this? If you don't have original replacement wire then you are in for a whole lot'a experimenting and testing. What I'm saying is the problem can be the wrong wiring just as easy as a bad ammeter gauge.
Hope this helped more than it hurt and good luck.
That's all true, but does not explain why my ammeter does what it does on 1.5V directly applied to the contacts on the ammeter with the harness unplugged.
Aw shucks All! If it's not a pure stock original car put the VOLT gauge replacement in. Not dependent on wire gauge, length, or position of the moon to work And they look identical to the original except they say VOLTS
01-26-2017, 10:18 AM
ammeter calibration
And they look identical to the original except they say VOLTS 