In that case I probably have done the same thing to my defroster switch - maybe knocked the connection loose. I think there is a relay that should click when you press the button, but I can't hear anything.
In my case I'm not all that bothered because the impacted cars sit inside both at home and at work. Also, to fill you in - in at least one case I've heard that the rear window shattered shortly after the defroster was turned on - and they are not cheap.
So, cruise control and rear window defrost are those things I can do without - and I suppose in the case of W123 that's a match with what goes wrong on the car!
Ken300D