Many thanks to member DOC, for transcribing the following service manual text. This text applies to electronic (not vacuum operated) cruise control systems in F and E series vehicles.
Speed Control Servo Assembly Connector
Speed Control Inoperative
A1 – Verify there is poser to the servo
- Disconnect the servo harness connector
- With the ignition switch in the on position measure the voltage between pin 7 (vehicle power) and pin 10 (ground)
- The voltage should be at least 12v
If yes, go to A2; If not, got to B1
A2 – Check for stuck stop light circuit
- With the brakes applied, check the voltage between pin 4 (brake input) and pin 10
- Is there 12v?
If yes, go to A3; If not, Stoplight switch is stuck on. Replace stoplight switch
A3 – Check brake/clutch circuit
- With the ignition switch off, measure resistance between pin 4 and pin 10
- Is the resistance at least 20 ohms?
If yes, go to A4; If not, Brake light bulb is blown or brake circuit is open. Service circuit including clutch pedal position switch
A4 – Check deactivator circuit
- With ignition off and no brakes applied, measure voltage between pin 9 (deactivator) and pin 10
- is there 12v?
If so, go to A5
A5 – Check for stuck on switch
- With no speed control switchs depressed, check voltage between pin 5 (command switch) and pin 10
- Is the 12v?
If so, go to A6; If not, replace switch
A6 – Check for switch operation
- With ignition off and steering wheel ON switch depressed, measure voltage between pin 5 and pin 10
- Is the 12v?
If so, go to A7; If not, go to D1
A7 – Check for stuck command switches
- With ignition off and no switches depressed, check resistance between pin 5 and pin 10
- Is the resistance greater than 3K ohms?
If so, go to A8; If not, one of the switches is bad, replace the switch
A8 – Check set/Accel switch
- With ignition off, depress Set/Accel switch and measure resistance between pin 5 and pin 6 ( command return)
- Is the resistance approx 680 ohms?
If so, go to A9; If not, switch no functioning, replace switch
A9 – Verify speed signal
- Raise rear wheels and operate at speed of 30 mph. Measure voltage between pin 3 (Speed Signal) and pin 10.
- is reading 4 – 5 volts?
If so, go to A10; If not service programmable Speedo/Odometer
A10 – Check for broken or bound actuator cable
- Remove speed control actuator from speed control servo. Check for broken speed control actuator by pulling on speed control actuator and noting throttle movement
- Is speed control actuator ok?
If so, replace stoplight switch; if not, or if binding or broken, service speed control servo
No Power to Servo
B1 – Check ignition circuit
- Make sure step A1 has been done.
- With ignition in the Off position, measure the resistance between pin 10 and a ground on the chassis.
- Is resistance less than 1 ohm?
If so, module power is okay, recheck A1; If not, there is a ground circuit open. service as required
No Power on Deactivation Switch Input
C1 – Check deactivator switch
- Make sure step A4 has been done
- Remove body harness connector from deactivator switch. Measure resistance between the two pins of the deactivator with no brakes applied
- Is the resistance less than 1 ohm?
If so, deactivator switch is okay, go to C2; If not, replace deactivator switch
C2 – Verify there is power to deactivator harness connector
- Measure voltage between pin 1 of the deactivator switch harness connector and chassis ground
- Is there 12v?
If so, go to C3; If not, Service blown fuse of deactivator switch
C3 – Check for open circuit between deactivator switch and servo
- Measure resistance between pin 2 on the deactivator switch and pin 9 on the speed control servo connector
- Is the resistance less than 1 ohm?
If so, repeat step A4; If not, open wire harness, service as required
Steering Wheel ON Switch Inoperative
D1 – Check for open circuit in switch ground
- Make sure step A6 has been done
- With horn depressed measure voltage between pin 6 and chassis ground.
- Is there 12v?
If so, replace On switch; If not, Open circuit or blown fuse in horn relay feed or open circuit in switch ground. Service as required, repeat step A6
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Doc
Speed Control Servo Assembly Connector
Speed Control Inoperative
A1 – Verify there is poser to the servo
- Disconnect the servo harness connector
- With the ignition switch in the on position measure the voltage between pin 7 (vehicle power) and pin 10 (ground)
- The voltage should be at least 12v
If yes, go to A2; If not, got to B1
A2 – Check for stuck stop light circuit
- With the brakes applied, check the voltage between pin 4 (brake input) and pin 10
- Is there 12v?
If yes, go to A3; If not, Stoplight switch is stuck on. Replace stoplight switch
A3 – Check brake/clutch circuit
- With the ignition switch off, measure resistance between pin 4 and pin 10
- Is the resistance at least 20 ohms?
If yes, go to A4; If not, Brake light bulb is blown or brake circuit is open. Service circuit including clutch pedal position switch
A4 – Check deactivator circuit
- With ignition off and no brakes applied, measure voltage between pin 9 (deactivator) and pin 10
- is there 12v?
If so, go to A5
A5 – Check for stuck on switch
- With no speed control switchs depressed, check voltage between pin 5 (command switch) and pin 10
- Is the 12v?
If so, go to A6; If not, replace switch
A6 – Check for switch operation
- With ignition off and steering wheel ON switch depressed, measure voltage between pin 5 and pin 10
- Is the 12v?
If so, go to A7; If not, go to D1
A7 – Check for stuck command switches
- With ignition off and no switches depressed, check resistance between pin 5 and pin 10
- Is the resistance greater than 3K ohms?
If so, go to A8; If not, one of the switches is bad, replace the switch
A8 – Check set/Accel switch
- With ignition off, depress Set/Accel switch and measure resistance between pin 5 and pin 6 ( command return)
- Is the resistance approx 680 ohms?
If so, go to A9; If not, switch no functioning, replace switch
A9 – Verify speed signal
- Raise rear wheels and operate at speed of 30 mph. Measure voltage between pin 3 (Speed Signal) and pin 10.
- is reading 4 – 5 volts?
If so, go to A10; If not service programmable Speedo/Odometer
A10 – Check for broken or bound actuator cable
- Remove speed control actuator from speed control servo. Check for broken speed control actuator by pulling on speed control actuator and noting throttle movement
- Is speed control actuator ok?
If so, replace stoplight switch; if not, or if binding or broken, service speed control servo
No Power to Servo
B1 – Check ignition circuit
- Make sure step A1 has been done.
- With ignition in the Off position, measure the resistance between pin 10 and a ground on the chassis.
- Is resistance less than 1 ohm?
If so, module power is okay, recheck A1; If not, there is a ground circuit open. service as required
No Power on Deactivation Switch Input
C1 – Check deactivator switch
- Make sure step A4 has been done
- Remove body harness connector from deactivator switch. Measure resistance between the two pins of the deactivator with no brakes applied
- Is the resistance less than 1 ohm?
If so, deactivator switch is okay, go to C2; If not, replace deactivator switch
C2 – Verify there is power to deactivator harness connector
- Measure voltage between pin 1 of the deactivator switch harness connector and chassis ground
- Is there 12v?
If so, go to C3; If not, Service blown fuse of deactivator switch
C3 – Check for open circuit between deactivator switch and servo
- Measure resistance between pin 2 on the deactivator switch and pin 9 on the speed control servo connector
- Is the resistance less than 1 ohm?
If so, repeat step A4; If not, open wire harness, service as required
Steering Wheel ON Switch Inoperative
D1 – Check for open circuit in switch ground
- Make sure step A6 has been done
- With horn depressed measure voltage between pin 6 and chassis ground.
- Is there 12v?
If so, replace On switch; If not, Open circuit or blown fuse in horn relay feed or open circuit in switch ground. Service as required, repeat step A6
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