The boost guage is controlled by a hose, just like the 740. The hose originates at the intake manifold under the throttle spindle cover, goes along the radiator fan shroud, and continues along the left inner fender and goes through the firewall under the brake booster. There is a rubber hose splice in the plastic hose near the left hood latch that sometimes seperates. Other common areas of problems are where the hose wraps around at the battery area.