Instead, the system consists of several parts, and troubleshooting a failure requires checking each:
* Cruise control switch (stalk): Located on the steering column. This is the most common point of failure. A faulty switch can prevent the system from engaging or maintaining speed.
* Brake switch: Located near the brake pedal. This is crucial; the system disengages when the brakes are applied. A faulty brake switch can cause erratic behavior or prevent cruise control from working.
* Clutch switch (if equipped with a manual transmission): A switch on the clutch pedal that disengages the cruise control when the clutch is pressed.
* Speed control servo: This is the actuator that controls the throttle cable. It's usually under the hood, near the throttle body, and can be tricky to locate and access.
* Vacuum lines: The system relies on vacuum to operate, and leaks in the lines can cause failure. Inspect all vacuum lines related to the cruise control.
* Wiring harness and connectors: Corrosion or damaged wires in the wiring harness can also cause problems. Check connections for corrosion and broken wires.
Replacing components: There isn't one "module" to replace. You'll need to diagnose the faulty component first. This involves checking for vacuum leaks, testing the switches with a multimeter, and potentially checking wiring continuity.
To replace a component:
1. Diagnosis: Determine which part is malfunctioning. A shop manual (Haynes or Chilton) for your specific year and model G20 is essential. This will give you diagrams and troubleshooting steps.
2. Access: Locate the faulty component. This will usually involve working under the dash (for the switch) or under the hood (for the servo).
3. Removal: Carefully disconnect any electrical connectors and vacuum lines. Take pictures as you go to help with reassembly.
4. Installation: Install the replacement part, making sure everything is connected correctly.
5. Testing: Test the cruise control system thoroughly after installation.
In summary: Don't expect to find a single "cruise control module." Finding and replacing a faulty cruise control component in a 1990 Chevy G20 requires patience, a shop manual, and potentially some electrical and mechanical skills. If you're uncomfortable working on your vehicle, take it to a qualified mechanic.
