I was driving last night and the radio started making this weird humming that went up and down with the RPM. I turned the radio off and kept going. I noticed that my interior lights were more dim than usual, and my headlights were pretty dim too. I tried the wiper and it was very slow. I was on the highway but was able to check at the voltage at the cigarette lighter without stopping and it was only showing 8 volts. Around this time the ABS light came on. Luckily it's diesel so it'll run I just won't have electrical power. I was able to make it home and the battery was pretty much dead.

I charged the battery today and drop tested it and it checks out. The battery light now stays on as long as the battery is connected, even if the key isn't even in the ignition. I ordered a new voltage regulator because that's what my instinct tells me, but I'm kind of stumped. The car can start with the battery charged and now shows about 12v while idling.

Am I on the right track? Oh, and the ABS light is now off.