If you meant a 1978 Chevrolet or GMC C-100, replacing the ignition switch is a moderately difficult job requiring some mechanical aptitude and the right tools. It's not a simple "plug and play" operation. Here's a general overview, but specific steps will vary depending on the exact trim level and configuration of your truck. Always consult a repair manual specific to your year and model for detailed instructions and diagrams.
General Steps (May Vary):
1. Disconnect the Battery: This is crucial to prevent accidental short circuits and electrical shocks. Disconnect both the positive (+) and negative (-) terminals.
2. Steering Column Removal (Possibly): Depending on your truck's design, you may need to partially or fully remove the steering column to access the ignition switch. This involves removing the steering wheel (requiring a special tool), bolts securing the column, and possibly other components. This is the most complex part and requires careful attention to detail to reassemble correctly.
3. Access the Ignition Switch: Once you have access to the steering column, you'll likely find the ignition switch mounted on the column itself. There will be several wires and possibly a locking mechanism connected.
4. Disconnect Wiring: Carefully disconnect all the wires connected to the ignition switch. Take pictures or make notes of where each wire goes to avoid confusion during reassembly. This is extremely important. A wiring diagram will be invaluable here.
5. Remove the Ignition Switch: The switch is typically held in place by screws or a retaining clip. Remove these fasteners carefully to release the switch.
6. Install the New Ignition Switch: Carefully install the new ignition switch, ensuring it's properly seated.
7. Reconnect Wiring: Reconnect the wires to the new ignition switch, matching them exactly to the way they were before. Double-check this step thoroughly.
8. Reassemble: Reassemble the steering column (if removed), the steering wheel, and any other components you had to disassemble.
9. Reconnect the Battery: Reconnect the battery terminals.
10. Test: Test the ignition switch to ensure it works correctly. Check all positions (start, run, accessory, etc.).
Important Considerations:
* Repair Manual: A factory repair manual or a Haynes/Chilton manual for your specific 1978 Chevrolet/GMC C-100 is essential. It will provide detailed diagrams and instructions.
* Tools: You'll likely need various tools, including screwdrivers, sockets, wrenches, possibly a steering wheel puller, and possibly a special tool to remove the ignition switch itself.
* Wiring Diagram: A wiring diagram is absolutely crucial to ensure correct reconnection of the wires to the ignition switch. Incorrect wiring can cause serious damage to your truck's electrical system.
* Safety: Work in a well-lit and ventilated area. Wear safety glasses to protect your eyes.
If you are not comfortable with this level of automotive repair, it's best to take your truck to a qualified mechanic. Improperly installing the ignition switch can lead to electrical problems, or even worse, create a dangerous situation.
