Here's a general guide. Consult a repair manual specific to your F-150's year and engine for precise location and wiring diagrams. A Haynes or Chilton manual would be invaluable.
1. Locate the Ignition Module:
* The ignition module is usually mounted on the distributor, but sometimes it's located separately on the firewall or near the coil. Your repair manual will show the exact location.
2. Disconnect the Wiring Harness:
* Carefully unplug the electrical connector(s) going to the ignition module. Take note of how they connect so you can put them back correctly. Some connectors may have locking clips; gently release them. Take pictures if it helps.
3. Remove the Ignition Module:
* The module is typically held in place by screws or a retaining clip. Remove these fasteners. The module itself might be a simple plug-in type or have some kind of mounting bracket.
4. Install the New Ignition Module:
* Carefully align the new ignition module with its mounting location.
* Secure it with the screws or clips you removed earlier.
* Reconnect the electrical connectors, ensuring they are securely seated.
5. Reconnect the Battery:
* Carefully reconnect the negative battery terminal.
6. Test the Ignition System:
* Attempt to start the engine. If it doesn't start, double-check all connections and make sure the new module is correctly installed.
Important Considerations:
* Distributor Cap and Rotor: While you're working in this area, it's a good idea to inspect the distributor cap and rotor for wear or damage. They're relatively inexpensive to replace and can cause starting problems if they're faulty. Replace them if necessary.
* Coil: A failing ignition coil can mimic symptoms of a bad ignition module. If replacing the module doesn't solve the problem, the coil might be the issue.
* Wiring: Carefully examine the wiring harness for any signs of damage, corrosion, or loose connections. Repair or replace any damaged wiring.
* Professional Help: If you're uncomfortable working with automotive electrical systems, it's best to take your truck to a qualified mechanic. Improperly installing the ignition module can damage other components.
This is a general procedure, and the specific steps may differ depending on your truck's exact configuration. Always refer to a repair manual specific to your 1991 Ford F-150 for detailed instructions and diagrams. This will ensure you have the correct information and avoid potential damage.
