Having a similar problem with the rear defroster on the '73 280 SEL. The fuse (on the firewall) checked and replaced for good measure. When the switch is pulled the switch lights up, but the rear window doesn't clear.
Where does the power feed connect to the heating element? On my window the element appears to run all the way to the edge of the glass, but I find no connection. When I do find the connection, how can I test the element?
73 280 SEL 4.5