Citroënvie member George Klein sent in these these pictures of repair work he has done on his SM time delay pot for the windshield wiper motor.
George says: “Amazing. Totally mechanical. Clean it and it works for an other 40 years. A bit of a brain surgery though. I had to repair because the harness wires to it because they started to melt.”
While many of today’s cars with intermittent windshield wipers have sophisticated optical sensors to initiate operation, Citroën was way ahead in the early 1970’s to an automated means of wiper operation. And for over 3 decades after the SM other cars with intermittent wipers relied purely on a time delay, in some cases variable as set by the driver.
The Citroën SM system adjusted the intermittent wiper delay based on the electrical current draw of the wiper motor. A wiper blade glides more smoothly over a wet windshield, using less energy, and a control circuit in the SM used that to indirectly determine if rain was present. Consequently the current flow to the motor is what George had to deal with but with a wire fix and a clean up of the delay mechanism, he’s good to go again with less complication and arguably greater longevity than the new electrical sensing systems.