Charging system problems

Hi... I'm hoping that someone out there can help me. I have an 84 190D with some kind of charging system problem. I was told that it could be the connection,the alternator, or the voltage regulator. The battery connection looked bad, so I replaced the terminals, but the problem was still there. The battery was tested, and it was good, but while the car was running, it was at 16 volts, and I was told that it should be at 12. The car was driven for four hours straight this morning, and everything was fine until it was turned off and needed to be started again, and there wasn't enough power in the battery. I would like to fix this problem myself, but with my limited knowledge, I'm relying on outside help to give me some advice. Could it be the voltage regulator? Also, a couple weeks ago all my blinkers died at once, as well as the guage showing the RPMS. The fuses are fine. Could that have something to do with the whole charging system problem? If anyone has any advice, I would be greatful. Thank you