I drive a 1983 Volvo 245 diesel. The alternator and battery are both less than 4 years old. A year ago, the battery light would not go out after starting. The alt is charging fine. A diode check was done and is normal, but I'm reading 30 AC volts across the pos and neg battery terminals. The AC volts between the alt output terminal and neg batt post are a few 10ths of a volt higher. I've been driving it a year now with no problems with the battery. Any ideas why the high AC voltage reading and is this causing the battery light to stay on, and how to fix it?