Well... I haven't been a Volvo owner for that long (couple of years).
I tried to reset the "service" light that comes up automatically after every 5000 mi. (I think) to remind one to have an oil change (which I do more frequently anyway) and this time couldn't.
It involves taking out a little rubber plug on the plexiglass covering the instrument panel (the plug is left of the speedometer on my '89 745T) and then pushing in a switch with something sharp (nail). Last time it did the trick, this time not. I tried when the light was on and also when it was off (it goes off after a few mn, it's just a reminder when one turns on the car).
Did I miss something? did I have to wait some time with the switch pushed in?

Note that recently the button that allows one to reset the clock's time (move the handles of the dashboard clock) doesn't work (I suppose it must be worn out inside). So I wouldn't be surprised if another switch was dead... any similar experiences anyone?