I recently hooked up a new head unit in my 1991 500SL, no amps or anything else just a head unit wired up to the speakers directly. Ever since then Im getting some squeeling when I run with the lights on at low speed at night. I am assuming the alternator either needs replacing, or it needs to be larger. I cant believe that the alternator would not handle just an added head unit.

The dealer is looking at it Thurs, but if they say the alternator is good, what are suggestions for a larger alternator that wont mess anything up.

I think I would try a new alternator belt before I spent anything on the alternator. The squeal comes from the extra load on the alternator causing a higher resitance to rotation. If the adjustment or condition of the belt was already marginal, the extra load caused by a, presumably, higher power ICE installation might be enough to make the difference.

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Cheers, Neil

The M119 engines are famous for needing new belt tensioners. I would think that for the belt to squeal that it must be loose.

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Thanks guys, it goes to the dealer today for service so I will have them check that.