Alternator

If on car run at 1500 rpms measure voltage from POS terminal at ALT (big red wire) should be 14.5 to 15.5 V if off car take to AutoZone they will test

Use a digital multimeter across battery posts, everything off. The generic spec for a full charge is around 12.6 volts. Start the vehicle, take second reading across battery posts, the second reading should be higher than the first if the charging system is working. If the second reading is not higher, check the voltage at the alternator bat terminal, if that terminal is higher, there is a problem with wiring circuit between alternator and battery. If the alt bat terminal is not higher, look for excite voltage to alternator, L terminal?