Seems if it were mine I'd make certain the alternator was in perfect condition before attempting to restart it. I've had bad luck several time with alternator shops putting in whatever relglators the thought may work well they didn't and in one case burnt several wires in my harness of a 123 617. For 50 bucks you should be able to order the right regulator as a start and have the alternator tested. Changing out several thousand dollars worth of computers is a frightening thought now that you know ripple is present.

Some vechiles do have factory installed capacitors but more so since the batteries are located far outside of the engine compartment and assist with load changes more so than ripple control.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

The R320CDI has the main battery under the front passenger seat.

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1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI