OK
You may also want to check to see what they have done at this resistor..
http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2EI1B4MYE2FA1DDHNT&yearid=1986%40%401986&makeid=MB%40%40MB&modelid=300%2DE%2D002%40%40300E&catid=G%40%40Cooling+System&mode=PA&subcatid=G5040@@Aux%2E+Fan+Resistor&source=www.peachparts.com&clientid=catalog.mercedesshop
This is behind the driver headlamp area and it is in the aux fan circuit..they burn the wires off and that will stop the fans.
They may have jumpered that section.
If those wires are intact, take a jumper from bat + and bring it over to each side of that resistor...one side should give you high fan and the other will be low fan...if YES, then fans/circuit are verified as OK from the resistor downstream, so your problem is upstream feed from the resistor.
I can guide you thru that after I have those test results .