electrical problem - 2000GT

I have a 2000GT with 117k miles that just recently developed a nice little habit of cutting off electrical service to the dashboard, instrument panel, radio(loses pre-set stations sometimes). Fortunately it doesn't kill the engine. This seems to be happening when the blinker/dim lights switch is used. not everytime though.
Anybody have that happen? and how do I isolate it without just buying parts?