2000 Chevy Impala

Test the alternator and battery, use a voltmeter and check output with and without the lights, leave the voltmeter attached to the battery and crank engine, you want at least 10 volts. Any lower and the battery is weak. Alternator should produce 13.8-14.8 volts with engine running. Any less and the alternaor should be replced as well. Then check all fuses and electrical connectors you can find, any corrosion or bent or pushed out pins should be fixed.