The oil pressure gauge isn't electrical, its got an oil line attached to the back of it.

Just run a ground wire from the back of the cluster to the main ground point behind the cluster.

Are all the flasher light bulbs good? if so then i'd blame the fast blinks on the relay.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg