Don,

Yeah, first check all connectors (left, right, front, and back) for bad ground/corrosions, as Aye Roll suggested. Sometimes (often) bulb connectors can melt and short some wires causing upredicatble behavior. If it is not it, then it is most likely that your flasher unit went south. I had this exact problem few months ago in my wife's S90. Turn signals and hazard lights worked intermittenly (stayed on most of the time). The problem was easily fixed by replacing the flasher unit, which is responsible for ... flashing turn signals and hazard lights. In late 960/S90 the flasher unit is attached to the hazard button on the front panel. You can carefully pry it out by using a very thin screwdriver (or similar object). Below is the picture of my (bad) flasher unit. The cost of replacement is $5x. I got mine from myvolvoparts.com. Hope this helps.

Raphael