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Recently after some major engine work, the ammeter in my 62 is no longer indicating a positive charge. It does reflect negative movement when turn signals are on or when the headlights are turned on. The system has been checked and the generator is producing adequate charge, it just isn't reflecting on the gauge.
Any ideas where to start looking?
Thanks in advance for any help.
You don't polarize a voltage regulator...you polarize the generator; the V/R merely provides easy access to some connectors for the process.
As noted, it just might be the case that the battery is fully charged. These full flow C1 ammeters are very simple devices..not really much to go wrong with them.
Last edited by Frankie the Fink; Sep 26, 2016 at 05:10 PM.
My 61 ammeter had the very same problem after we reassembled it post painting. The tech had rewired the instrument pod according to the schematic which according to the shop owner (a 30 yr C1 restoration expert) is wrong regarding the ammeter.
So we reversed the ammeter wiring putting the 4 red leads on the passenger side post and 1 black on the drivers side post. Since then, it reads as it used to; slightly positive reading with a small drop when brakes are applied or lights are turned on.
Results may vary!
Last edited by 61 Roadster; Sep 26, 2016 at 05:34 PM.
If the OP can pull out his headlight switch and engage high beam and the ammeter deflects to the left ("-" side) then its wired correctly; but yes; the original GM schematics are wrong. Dr. Rebuild sells correct schematics.
With a good battery and a healthy charging system needle deflection when underway should be almost nil. Here is my '61, at speed, with a 600W sound system thumping away...note the ammeter.
The speedo and tach read correctly - the car has a 5-speed Tremec with overdrive
Last edited by Frankie the Fink; Sep 26, 2016 at 05:49 PM.
In my case, the ammeter would only reflect negative readings on the dial. It would read zero, then drop if you stepped on the brake or turned on the lights. In other words, it could only move left of zero; never any positive reading in spite of confirmed charging to the battery.
After we reversed the wiring, it now reads both negative and positive again.
Troubleshooting the ammeter circuit can be difficult. The following applies to cars equipped with alternators. In the Chassis Service Manual there will be a simplified diagram of the charging system similar in part to that show above.
Possibly the biggest mistake that people make associated with the ammeter circuit is not turning the ignition switch to either ACC or ON when trying to decide if the ammeter is showing proper discharge. You can perform the following test and see if it makes a difference
. Start the engine and let it run for a few minutes until the ammeter reads close to zero. Shut off the engine and with the ignition switch OFF, turn on the high beam lights. Make a note of the ammeter reading. Turn off the headlights. Turn the ignition switch to ACC and again turn on the high beams. The amount of discharge shown by the ammeter should be about twice, or more, what it was before.
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 and the voltage regulator.
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.
The voltage regulator is set to have a voltage slightly higher than the fully charged voltage of the battery so that the alternator will carry most of the vehicle loads and maintain a slight trickle charge on the battery at all times the engine is running. Under normal conditions, the ammeter will show a slight charge when the engine has been running for a few minutes and the system is working correctly.
Uh - that's more applicable to a C2 which uses an alternator and does NOT use a full-flow ammeter. Rather it measure current differently via a shunt from the horn relay to the starter - in effect its measuring voltage.
Uh - that's more applicable to a C2 which uses an alternator and does NOT use a full-flow ammeter. Rather it measure current differently via a shunt from the horn relay to the starter - in effect its measuring voltage.
From: Las Vegas - Just stop perpetuating myths please.
Low post count, lack of participation, little or no profile, and a old or archived thread has burned me so many times I can't forget. Yes, troll profiling and I'm guilty!
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Ammeter Help Needed
