On these cars it is frequently just the regulator. It's a cheap repair under $20 and takes no more than 10 minutes from start to finish. You'll need a 13 mm wrench to disconnect the battery and a stubby flat screwdriver to remove the two screws holding the regulator. BTW, the parts store will have it listed as an internal regulator. I find that technically inaccurate. It's more of an integrated regulator since it mounts to the outside of the alternator. I suppose in the "parts store" lexicon an external regulator is one that mounts to the car body (like the old Fords, oops I'm dating myself).