I seem to remember reading sometime back on one of these posts that the aux water pump can short out internally and cause blown traces. I've been thinking that it might be a good idea to isolate some of the loads on the climate control by adding a relay and separate fuse to the fan circuit and the aux water pump circuit. This would ease the load on the climate control unit and also make it easier to troubleshoot, as a blown fuse in one of the relay circuits would isolate the defective part.

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C