Inspect your battery negative (ground wire) at the engine block. After 10 years, the OEM Negative cable becomes brittle and creates a high resistance (hot spot) at the cable connection to the engine block. It is often the most overlooked item when troubleshooting the charging system.
You can have a custom Negative side post terminal fabricated using 2 ga. battery cable, and you can save money if you remove your old cable and take to a shop equipped to make them. A welding supply shop is an possible option. Be sure to order extra grounding connects [at the battery terminal], too. You should have at least 2 if you want to upgrade the sound system in your Sunbird.
Your other option is to purchase a service replacement, which you can order from most auto parts sources.
Unless there are visible signs of damage or any evidence of a white powdery residue near the ends of the positive cable, the cable usually doesn't need replacement.
Just install a new battery stud in the terminal, if yours is worn.