Probably caused by buildup inside the switch. Get a can of "electrical cleaner" from Autozone, and hose down the area at the base of the stalk.
Check this thread out, but you probably can get away without disassembling everything. Just stick the hose into the right area and spray away, then work the switch back and forth for a bit.
http://www.rx7club.com/showthread.ph...dlight+cleaner