The 5th port on your vacuum selector switch (not labeled on your paper towel) goes to the speedometer to control its 2-speed reduction unit which keeps the speedometer reading correctly in both high and low range.
Mike B
Mike Boteler
1956 Chevy 3100 Resto Rod 1952 Willys M38 Army Jeep 1983 Jeep CJ7 Laredo 1984 Jeep CJ7 +++++ Silver Spring, MD