I believe on the early style cluster the 1 terminal on the back of the
tach took a single black wire directly from the - side of the coil. IIRC
the + side of the coil was brown from the ballast resisitor and the
negative side was black, later changed to white with a red trace. The
wire may have come loose when you snapped the cluster out. The positive
and negative feeds come from the round plug.
Bob
