I am having the same problem with my 1992 300SD. In addition to the instrument cluster lights flashing periodically when using the turn signal they also flash when using the windshield wipers. The frequency of occurrences is highest when the wipers are set on "Intermittent." They flash approximately every 26-30 seconds during light rain, when my wipers are set on Intermittent. Much less frequently when the wipers are set on Normal or Fast. After the cluster of lights flash, the seatbealt warning light flashes four times.

Anyone with ideas? The dealer hasn't been able to replicate the problem, but it happens every day when I am driving.