What should the ammeter read?

[69autoXr]

Hey everybody,

The ammeter in my dad's 70 automatic (with 55 amp alternator) always reads a negative amperage. Is this normal? I would've thought it would read positive, whatever amperage the electrical system is drawing. He hooked up an auxiliary guage at the horn relay and it read zero. There are no electrical problems, but we want to make sure the guage is working correctly, and I would like to know in particular what the ammeter should read.

Thanks,

Chris

 

[ChuckG]

If your alternator and charging system are working, AND if the gauge is OK, the ammeter should show a slight + reading while you're driving.

If you turn on the headlights, for example, you should see the needle deflect negative, then go back to "0" or slightly positive again. If you have to spend a lot of time cranking the engine, after the engine fires over, the ammeter will show a larger + charging rate, maybe 20 amps or so, and then come down slowly as the battery charges and hover around the positive side of the zero marking. I'd check the alternator. Most auto stores like PEP Boys, etc. will check your alternator for free. If originality is of concern to you, many Corvette businesses can rebuild and detail your original alternator. Chuck