It is possible that the relay is broken...I presume that the check-light is not lit either when you switch the rear defroster to on?
The relay in the 190 is a combined relay as well. It controls the rear defroster, window wiper and indicators. It is located under the plastic cover of the fuse box. Unlock the front and squeeze the rear pins (U-shaped) together to get the ends out of the fuse box housing. If the U-pin is out of the black fuse housing (still connected to the plastic cover), you can remove the plastic cover.
Did you check power at the switch connector?
with a minor 600+k