Why not just get a cluster with the tach from a V6? Should plug in, same transmissions are used. At least one Mystique person I've seen posting has a cluster with tach in a Zetec car, and in Australia they have a tach for the Zetec.
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2 Red Tours!
'96 GL V6 ATX - the wifes ride
'98 SVT with both options - my toy!
OF's TH fix / K&N / Glove Box Light / an dats it!