If your headlights get brighter, you voltage regulator is going bad. Replace it, if the voltage gets to high your battery gets overcharged. This ruins you battery and can be dangerous to.

It may even solve the erratic reading from you meters.
5 minutes job and not very expensive. I would advice to get a genuine Bosch regulator, cheap ones often burn out quickly.

Wait until the engine is cooled down, very close to the exhaust!!!.

Rob