* Wiring Harness Issues: Despite replacing parts, a damaged or corroded wire in the main harness could be preventing the signal from reaching the coil. Inspect all wiring, especially the connections between the ignition switch, ignition module, coil, and distributor. Look for breaks, chafing, corrosion, or loose connections. Pay close attention to the ground wires. A poor ground can cause all sorts of electrical gremlins.
* Ignition Switch (Even though you replaced the cylinder): While you replaced the lock cylinder, the ignition switch itself (the part that actuates when the key is turned) might still be faulty. It's a relatively common failure point.
* Ignition Module (Double Check): You mentioned replacing the ignition module, but ensure it's the correct one for your specific engine. Also, double-check its installation and that it's properly grounded. A faulty module, even a new one, can be a source of the problem (though less likely if you got it from a reputable source).
* Cranking System Issues: Although you replaced the starter relay, ensure your battery is fully charged and has good cables. A weak cranking system (low voltage) can sometimes prevent spark. Test the battery voltage while cranking. It should be above 10 volts. Below that, the ignition system won't have enough power.
* Distributor Issues (Beyond the Pickup): While you've replaced the pickup coil, there's more to the distributor than just that. Check the distributor cap and rotor for cracks or carbon tracking. A worn or damaged distributor shaft can also prevent proper operation. Ensure the distributor is properly timed (although this won't prevent spark entirely, it could weaken it to the point of being undetectable).
* PCM/ECM (Computer): Less likely, but a faulty Powertrain Control Module (PCM) or Engine Control Module (ECM) could prevent spark. This is harder to diagnose without specialized equipment.
Troubleshooting Steps:
1. Battery Voltage Test: Check the voltage at the battery terminals while cranking.
2. Visual Inspection of Wiring: Carefully examine all wiring related to the ignition system for damage or corrosion. Pay special attention to ground connections.
3. Test for Power at the Coil: With the ignition key turned to the "on" position (but not cranking), check for 12 volts at the positive (+) terminal of the coil. If there's no power, trace the wire back to the ignition switch.
4. Test for Ground at the Coil: Check for a good ground at the negative (-) terminal of the coil.
5. Check the Ignition Switch: This is best done with a wiring diagram and a multimeter. You need to check for the correct power and signal going to the coil and ignition module when the key is turned to the "start" position.
6. Distributor Cap and Rotor: Inspect for cracks, burns, or other damage.
7. Consult a Wiring Diagram: Obtain a wiring diagram specific to your 1986 Ford Bronco II and use it to trace the entire ignition circuit. This is crucial for systematic troubleshooting.
If you're uncomfortable working with automotive electrical systems, it's best to take it to a qualified mechanic. Further diagnosis without a multimeter and a wiring diagram will be difficult. Remember safety first – disconnect the negative battery terminal before working on the electrical system.
