golf mk1 convertable

wonder if anybody can help me,just restoring a mk1 golf gti convertible,put a second hand speedo,instrument cluster in and all works fine apart from when I hit 2000 revs the oil light starts flashing and buzzer comes on,have had car serviced and changed all oil switches,have ran a separate earth to clocks and still comes on,have disconnected switches and still comes on,have I bought a faulty cluster or can anybody advice me of what this could be

Make sure the connections on the speedo are tight, as well as the voltage on your clusters 10V stabilizer.

Verify that pin 14 black has 12V battery both sides as well as pin 2 (brown) is ground, and that wouldn't hurt to add a ground to frame right there, as well as placing a piece of electrical tape under the mylar.  Remove the main connector shroud, carefully lift the mylar, and run one piece of tape over the tongue pad side to tighten up the connectors.  

Yes cluster are known to be iffy.

check the oil pressure switch in the filter housing, it should be 1.8 bar rating. VW switch would be white, but pattern parts often dont follow VW colour coding. the wire colour should be black/blue, but if its had work on the loom it may be yellow

check the dash earth to the side of the head, its the brown/white with a ring terminal