The switch gets worn out. If it's the original switch, it's 18 years old and the moving parts of the switch have been moved a minimum of 2-3 times a day every day for 18 years. They don't burn up, they just wear out.
Here's a sure fire way to confirm the switch is bad. Next time your A/C blower quits or your turn signals don't work, gently turn the key back until you feel a little resistance. Don't shut the car off, just ease the key back with about the same finesse as if you were disarming a bomb. about the time the key reaches a stopping point, the signals should start working again, along with the A/C blower.
On my '91, it happened every time I hit a pothole or bump in the road. The blower fan would quit working and I went straight into WTF?? mode. Took me a while to figure it out. I had my hand on the key a little longer after starting the car and noticed that when it moved, the fan quit. I rolled the key back just slightly, and the fan came back on. I still haven't changed out the switch, I don't drive the car as much anymore and it's about to come apart for paint/body and new engine. so I just deal with it when I drive it. | 
