OK

I am assuming you tested the fuses I mentioned ???

Behind the headlamp [ don't know which b/c you have RHD], there is aux fan Resistor..the wires burn off,,check that for the next test.

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2GN17VPXQ2GO19XIJQ&yearid=1989%40%401989&makeid=MB%40%40MB%40%40X&modelid=260%2DE%2D001%40%40260E&catid=G%40%40Cooling+System&mode=PA&subcatid=G5040@@Aux%2E+Fan+Resistor&source=www.peachparts.com&clientid=catalog.mercedesshop

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A Dalton