One more F600 dash question

[Bobaloo2]

Will I need the large gear reduction thing that was attached to the F600 speedo? Should I connect my speedo cable to it and attach the "ground wire"?

[FORDification]

You don't need that. It was used on trucks with two-speed differentials, to keep the speedometer accurate when alternating between the two different final drive gear ratios. Just throw it away and hook your cable up directly to the speedometer.