The dash lights in my wife's 1988 240 exhibit a strange behavior - every now and then the dash lights dim, and the turn arrows (both) glow, along with the high beam indicator light and the rear fog lamp switch. When this happens, often the turn signals don't work. But as soon as you switch off the headlights, the turn signals begin to work. I know this sounds like some sort of electrical short, but I was wondering if it's indicative of anything more specific.

Thanks!