Basic wiring will be one wire (blue iirc at least for 67) that comes from the fuel sender in the rear light harness to the kick panel,then to the dash harness.
The dash harness has a connector round in the case of ralley dash that will have that same wire.
Once into the cluster the circuit boards take it to the correct pin on the gauge.
As corny as this is it is very well done from an understanding sense