The wiring harness on that car (all 93 - 95 MBs) is very prone to failure - do a search here, there are plenty of threads.

You could ask him what codes were retrieved or retrieve them yourself using the push-button/LED combo on the diagnostic module.

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE