To check the alternator take your volt meter ground the neg. and touch the pos. on the large lead coming out of the back of the alternator with the engine running you should have charging voltage 13.5 or more volts. If you have 12v or less you may have a alternator problem. Form here move the battery iwth the engine running and make sure you have 13.5 or more volts. If not you probably have an regulator problem. Not sure how right on I am for MB but all my old Mopar stuff worked like that