Packard Forum Index » Pre-War (1899-1942)

Rusty says The only way for the ammeter to read in reverse is if the battery is reversed.

There is another reason: If the ammeter reads in reverse with the battery connected as positive ground, then the ammeter leads have been reversed.

Update today.

Repolarized as per the instructions. Small spark.

Cranked car and the ammeter still pegged to left showing "discharge." Turned ignition off, and removed key. Ammeter is now "zeroed out" as it was before.

When disconnecting battery, no spark and now reaction at ammeter. No headlights or radio on.

The thing I still don't understand is that with the old battery the ammeter showed a charge and now it shows a discharge.

Does it make sense to put a good digital meter in the circuit to make sure that there are no problems with the ammeter?

O_D May have given the answer above. Is there any chance the old battery had been reversed and you correctly put the new one in. With nothing running, what happens to the amp meter when you turn the headlights on? If it's reversed, it would show a charge.

You can place a voltmeter on the battery terminals. With nothing running, you would see battery voltage or roughly 6.3v but if running and the generator is charging you should see something in the range of 7-7.5v. If you still see the 6v then there is something wrong with the charging circuit.

Here are the numbers:

Battery is at 6.28 V
When running, charge at battery terminals is 7.70 - 7.83V.
High beams drop to 7.12V.

Car ignition off and headlights on sends ammeter to positive charge.

Thus, apparently the ammeter leads are reversed.

That's good to hear. Question now is why. If the ammeter was rewired, apparently someone went to the trouble to reverse the battery to get a negative ground. Maybe because they didn't know it should be positive or was there some solid state component or accessory that needed it. Only solid state component I can think of that would possibly be installed on the car would be a solid state radio vibrator replacement or something else to do with the radio. If not that, then possibly some kind of charger or aftermarket adapter that plugged in to cigarette lighter.

Quote:

Technically you are correct. But the questioner does not mention reversing the ammeter wires. I think he would remember if he did this. He also seems to think this is a new problem, one that did not occur before changing the battery. Therefore the battery seems the likely culprit.

If you want to get real technical there is yet another way to get an ammeter to read in reverse.

It is possible to charge a battery BACKWARDS in other words, change the + to - and the - to +.

A friend had this happen years ago. He accidentally left the lights on in his Triumph TR3, killing the battery. A tow truck gave him a boost and he got in the car and drove about 50 miles.

Unknown to him the tow truck driver who was not familiar with English cars (+ ground) had connected the jumper cables wrong way round. On starting the car the generator became polarized in reverse and the flat battery charged up backwards.

He also told me if this ever happens do not try to change the battery back. You may get away with reversing the polarity once but if you try to do it again you will ruin the battery.

Rusty writes:
"It is possible to charge a battery BACKWARDS in other words, change the + to - and the - to +."

GOOD catch rusty!!! That's probably what happened. Old battery had terminals reversed and/or ammeter reversed too.

Look at the voltage regulator to see if it states + or - ground.

Edit. Also check VR for 12v or 6v label.

Rusty says But the questioner does not mention reversing the ammeter wires. I think he would remember if he did this

Rusty, I didn't think the current owner reversed the ammeter wires. I'd bet a prior owner did it at the same time he installed the battery with reversed polarity. Perhaps when the prior battery was removed and the new battery was installed the current owner didn't notice the old one was installed with negative ground. I think that would explain why the problem only happened when the new battery was installed.

Sounds like this problem is resolved.