[jhv48]

Just went through this with my SPF.
Your ammeter is telling you that you’re running your car off of the battery. Your alternator is either not operating properly or you have a wiring problem and the charge is not getting to the battery. Easy to test.
With all switches off, connect a multimeter to the poles of your battery and see what your battery voltage is. Should be around 12.6 volts. If not, battery needs a charge or is going bad.
Now turn on the engine and read the battery again. Should read between 13.7-14.7 volts. If not, then your alternator is not putting out enough current to keep your battery charged. Or the charge isn’t reaching the battery from the alternator. Put the multimeter on the one wire pole at the back of the alternator with the engine running. Should read between 13.7-14.7 volts. If not, alternator needs replacement.
A third culprit, and one that happened to me is that the fuse box wiring under the dash was loose and the charge wasn’t getting from the alternator to the battery. Not fun chasing that one down. Had to have a shop that specializes in hot rod wiring find that one.
And my ammeter always rests on the left side of the center Mark even when no draw is present. Has done that since new, 11 years ago.
A cheap multimeter will help you isolate the cause.