Now In the gauge cluster Resto phase. Amp gauge is on constant 0. Maybe slight to the right on the +40 side. When load is placed on, headlights,fan,radio needle stays at that constant position. Even at increased rpm. Is that normal operation? How can I check if gauge is functioning properly?

 

Amp gauges are a poor idea, next to useless, something has to be pretty well RONG for the thing to say much.......

much better off with a voltmeter from a 80's Silverado pickup junk yard style, mounts the same and similar/close print, tape off the amp meter wires, and take a wire from either yellow or brown for the +12 on the VM and of course ground the other side, like it was a lightbulb....

 

Ammeter shows the actual current flowing to or from the battery, and thus is the best indicator of charging circuit condition (alternator output, battery condition and wiring condition). A voltmeter will only indicate the output voltage from the alternator.
With engine off, turn on the headlights. The ammeter should show a discharge. Immediately after cranking and starting the engine, the meter should show a high charge rate. If the meter does not deflect, there is a problem with the meter circuit(burnt fusible links, bad meter or a cut wire).

 

I'm not a big fan of ammeters as well.

The other issue- if you have upgraded/added- fans/AC/stereo amp/higher output alt/larger gauge wire- then the OEM Ammeter won't read correctly anyway.

I changed mine over to a voltmeter w/ the green lettering for my 71.

DSCN5233 by Richard Hayes, on Flickr

 

Im going to go out on a limb here.... Where are the fusible lincs located?

 

Did u use the same ammeter plug or did u have to rewire?

 

If you have torched a fusible link- you'll have more problems than just your ammeter not working. There's one off the starter solenoid/horn relay and the alternator (not sure about later years).

The voltmeter just requires a ground ( cluster gauge ) and a switched ignition source- the pink wire off the fuel gauge or water temp gauge will work fine. So it's really no re-wiring required and just can leave the ammeter plug disconnected.

Richard

 

Additional note: on the"battery" gauge it's actually not really an amp gauge, it's a galvanometer that simply measures the differential running voltage between the horn relay 12v and the 12v wire on the starter;
very small current runs thru it.

A real amp gauge actually passes the full power of the car thru it. (in series with the full battery load). If the amp gauge fails your car is totally dead. not the case with the C2 or C3 gauge.

 

To bench test your battery (amp) gauge:
Connect a ground to the TOP terminal and just touch 12 volts to the BOTTOM terminal, the needle should deflect DOWNWARD.


Connect ground to the BOTTOM terminal and just touvh 12 volts to the TOP terminal, the needle should deflect UPWARD.

There are three fusible links listed in this schematic, one near the starter solenoid another near the alternator and the third at the horn relay.

http://www.vetteprojects.com/bmv/mis...tte%201971.pdf

 

Additional info:

By referring to the above diagram, it can be seen that the ammeter reads the difference in voltage between the battery and the alternator. The wire that goes directly from the battery to the alternator and appears to short out the ammeter is a meter shunt. What the ammeter actually reads is the voltage drop across this wire. The resistance of this wire is about 0.1 ohm. There is no physical resistor in the circuit, the resistance is due to the length of the wire required to get from the starter solenoid to the horn relay around the engine bay. The horn relay is not in the ammeter circuit but is a convenient connection point for the alternator output alternator. When the output voltage of the alternator is greater than battery voltage, the ammeter shows a charge proportional to the difference in voltage. When the battery comes up to full charge, the ammeter drops to near zero. If the output of the alternator is less than the battery voltage, as under a heavy load, the ammeter will show a discharge proportional to the difference in voltage

You can test the gauge with a AA Battery by hooking it up to the gauge.

 

Thanks to all. Pull out gauge tomorrow. Start with testing the ammeter. Then fusible lincs.

 

Hi Richard. Was wondering what model volt meter will fit in 71 bezel? I believe volt meter in Vette didn't start till 77. But the face is totally different than the green gauges. Thanks.

 

I had Corvette Instrument Services in Florida do the conversion for me-
71 as well. So no issues w/ fitment.

Sorry don't remember what it cost as my car is in it's like 6th year of resto-moding...

Richard

 

You really do get more information as to the status of the charging system with an ammeter. If a cell opens or the battery becomes sulfated, the charging current will drop to a very low level, but the voltmeter will still show alternator output voltage.

 

below is the post I made after locating and replacing the burnt fusible link in my 68. Yours may be similar, but if not, you will get the general idea. I would suggest checking the fusible links before pulling the dash to check the ammeter.... it's quite easy to eyeball them and see if they're "open".


https://www.corvetteforum.com/forums...locations.html

 

Ok. With a grounded continuity light, I tested both contacts at ammeter and from plug attached to meter. (Both contacts provide power to meter as continuous power loop I'm guessing?) However, both sides getting power. Bench tested meter as directed above. Needle not budging. Time to order new guage? Unless I'm missing something?

 

OR you can do this- repair it-

https://www.corvetteforum.com/forums...procedure.html

 

Thanks for the Linc. I'll give it a go tonite.

 

Got meter apart. 45 years of crud under case but no broken wire. Cleaned up with brush and compressed air. Gauge now responds to battery test. Poxy back on case and reinstalled back in car. slight movement with load on. Guessing that's the norm.

 

A LOT of mis-information in this thread. Ammeters are fine; just as voltmeters are fine. If you want to know what voltage your main-trunk line is seeing, use a voltmeter. If you want to know what amperage that line is seeing, use an ammeter. Both are 'good', but they tell you different stuff....IF you know how to read them (especially ammeters).

When your battery is charged up completely and the engine is running, the ammeter SHOULD read ZERO, of very close to it. Just after you start the engine, the meter should move to the 'discharge' side of zero. If your battery is in good shape, it won't be very far from zero; if the battery is old, it will move farther on the discharge side.

As the alternator charges the battery, that offset from Zero will lessen with time...unless the battery is almost "toast".

Also, that ammeter does NOT have full line currect running thru it. It measures the voltage drop (millivolts) over a fixed length of main-trunk line, but it reads amperes because of the dial scaling. You can use a AA or AAA battery to QUICKLY send signal to the ammeter...just to see if the meter works...then remove leads so the fine connecting wires inside do not FRY.

If you have other questions, send me a PM.