1975-77 Models

Check sensor terminals at back of speedometer for proper connections. Block front wheels and jack up one rear wheel off ground. Release parking brake and place transmission in Neutral.
Unplug wiring connector from computer. Using a 10 ohm resistor, connect positive lead of ohmmeter to computer connector speed sensor terminal. Connect negative ohmmeter lead to a known good ground.
Have an assistant turn rear wheel slowly and observe voltmeter. Ohmmeter should fluctuate near infinity mark. If not, replace speedometer assembly if wiring is not defective.

Fig 1: Vacuum Control Valve Test
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: Vacuum Switching Valve Test
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 3: 1978 20R Engine Throttle Positioner System
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 4: 1978 2T-C Engine (California & High Altitude) Throttle Positioner System
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 5: 1978 2F Engine Throttle Positioner System
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 6: 1978 4M Engine Throttle Positioner System
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 7: 1979 Throttle Positioner Systems
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002