Hi, the rear SAM does not control the front wipers. It looks to me as though the rear SAM was replaced unnecessarily. I've attached a function description of the wiper operation below. Please let me know if you have any questions.
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The wiper system is operated using the combination switch (S4). The selected wiper level for (front) wiping is transmitted by the steering column module (N80) to the front SAM control unit (N10) via class B CAN. For rear wiping the selected wiper level is transmitted by the steering column module to the central gateway control unit (N93) via class B CAN to the rear SAM control unit (N10/8), which actuates the tailgate wiper motor (M6/4).