Alternator is the part that keeps our battery charged and powers lights, radio, and gauges when the engine runs. We mount it on the engine with a belt so it spins every time we drive. Inside, coils and magnets create electricity, sending power back to the battery and electrical parts. If it fails, the battery drains and lights dim, hello dark ride. We test its output and replace brushes or belt if needed. We fix it before it dies, simple as that.