1978 240d Rear defroster button iluminates and times out but defroster does not clear window at all. I am assuming it turns on a timing relay like the glow plugs do , Who can tell me where this relay is located so I can check it out to see if it is the problem. There do not appear to be any broken wires in the grid on the window , I have not dug out my meter to check for power at the rear wires but they appear in good shape and the connections on either side seem undisturbed . Any help or suggestions will be appreciated

I fairly recently did this drill on both of the 1980(s) MBZs below and both had littly to no remaining continuity in the heat elements that are glued to the inside of the rear window... and it very easy to check this by disconnecting one of the spade connectors on either side and then check for continuity .

And IF it is the window elements you have two choices...
(1) the tedious task of trying to repair and this IMHO is NOT practicable unless you are prepared to remove the glass and turn the inside to the upside so you can work many tedious hours cleaning and repairing the elements by literally masking and repainting new elements over the top of the existing oxidized elements, OR
(2) replacing a very expensive windshield [I don't remember the $]

P.S. - I think I found the relay under the dash or console!?