1979 Ford Bronco F100-F350 Vacuum Systems Trouble-Shooting Guide & Tools

This is page 44 of a Ford service reference document (album titled "1979 Bronco F100 through F350") introducing the Vacuum Systems section. It explains that vacuum trouble-shooting follows the same basic rules as electrical trouble-shooting, weighing probability, speed, simplicity, elimination, and certainty. The page outlines four fundamental diagnostic steps: verify the condition (duplicate the malfunction before repairing), perform a quick visual inspection (look for obvious issues like a disconnected hose), think simple (low vacuum readings are often caused by loose, crimped, or slightly cut hoses; intermittent problems by something loose rather than broken), and don't assume (curing a symptom may not address the root cause, and new parts aren't necessarily good parts). It describes two trouble-shooting tools: the vacuum gauge, used to measure vacuum in supply lines, components, and reservoirs and detect fluctuating supply or leaky hoses; and the vacuum tester (Rotunda 21-0014 or equivalent), which creates a specific amount of vacuum for testing circuits and components, with the needle dropping to show vacuum decrease when a component functions. Four photos show the typical gauge and tester and their use. A color designation legend defines hose/wire color abbreviations: bk-black, b-blue, g-green, t-tan, r-red, w-white, y-yellow.