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1979 Ford Bronco F100-F350 Speed Control Wiring Diagram & Troubleshooting
Reference · 1978-1979 BroncoAll 116 wiring diagrams
Speed control wiring/operation page showing the servo, amplifier, speed sensor, switch positions (Off/On/Set/Coast), check valve and vacuum reserve tank, plus trouble-shooting steps.
Part of 1978-1979 Ford Bronco Wiring Diagrams
This page (page 47) from a Ford electrical/vacuum troubleshooting guide covers the Speed Control (cruise control) system for 1979 Ford Bronco and F100 through F350 trucks. The 'How It Works' section lists the system components: an OFF-ON switch, SET-ACC (accelerate) and COAST switches, a throttle actuating servo, an amplifier assembly, a speed sensor, linkage, a check valve assembly, and a vacuum reserve tank with hoses. Operating instructions explain how to engage the system above 30 mph, adjust speed up or down, and disengage it. A Trouble-Shooting section provides a visual inspection checklist covering frayed wires, damaged vacuum reserve tank, worn hoses, speedometer cable binding, servo/throttle linkage binding, and bead-chain free play exceeding ¼ inch, with the advice to see an authorized Ford dealer if problems persist. The wiring diagram shows current flow from the headlight switch (hot at all times) through connector C713 to the horn relay, from the ignition switch through Fuse 10 (20 Amps), and from the stoplight switch to the speed control amplifier. It maps the horn switch, speed control switch (positions: Off, On, Set, Coast), speed cable sensor, and throttle actuator with its modulating valve and servo motor. Wire colors (y/gr, bl/y, bl/bk, bk/gr, r/bk, w/pk, gy/bk, o/y, br/gr, y/r, p/bl) and connectors (C301, C305, C713, C715, C716, S601, G703) are labeled.
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Frequently asked questions
- What fuse protects the speed control system on a 1979 Ford Bronco/F-Series?
- The diagram shows Fuse 10, rated at 20 Amps, fed from the ignition switch (hot at all times), supplying the speed control amplifier via a bk/gr wire.
- What are the positions of the speed control switch?
- The speed control switch has four positions: 1) Off, 2) On, 3) Set, 4) Coast.
- How do you operate the speed control system?
- Drive at least 30 mph, turn the OFF-ON switch to ON, then quickly depress and release the SET-ACC switch. To decrease speed, touch the brake and reset or push COAST and release at the desired speed; to increase speed, touch the brake and reset or push SET-ACC. To turn it off, switch OFF-ON to OFF or touch the brake pedal.
- What should I check if the speed control operates erratically or intermittently?
- Check for frayed wires, a damaged vacuum reserve tank, damaged/worn/poorly fitted hoses and electrical wires and connectors, speedometer cable binding or improper connection, binding at the servo and throttle linkage, and free play in excess of ¼-inch in the bead chain.
- What connectors are used in the speed control circuit?
- The diagram labels connectors C301, C305, C713, C715, and C716, splice S601, and ground G703.
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