I went through this on my old 90'. For me it turned out to be the replaceble printed circuit board that slides into the back of the instrument cluster. I believe it is a voltage regulator for the guages. I ended up replacing my sending unit first unfortunatly. I bought both parts from the local Ford parts house. Good luck, Dave.
347, AFR 185, FTI cam, Systemax, shorties, 2.5'' exhaust, stock airbox, 70mm tb, 75mm MAF, 24lb
387rwhp, 397rwtq, email@example.com first passes, more track times soon