* Ignition Coil: A cracked or failing ignition coil can arc internally when moisture provides a conductive path. This would explain why it works better when wet (the moisture improves conductivity, weirdly enough, until it's so bad it shorts everything out).
* Wires/Connectors: Look closely at all the ignition system wires and connectors, particularly those running to and from the coil, distributor, and ignition switch. Corrosion, cracks, or damaged insulation can cause intermittent issues exacerbated by moisture. Pay special attention to places where wires might rub against metal.
* Distributor Rotor: While you replaced the cap, the rotor inside the distributor may also be cracked or worn, allowing moisture to bridge gaps and create a short.
* Pick-up Coil (inside the distributor): This component in the distributor is crucial for generating the ignition signal. Moisture could be interfering with its operation. Often, this requires distributor replacement, not just cap and rotor.
* Crankshaft Position Sensor (CKP Sensor): While less directly related to the distributor, a failing CKP sensor can cause intermittent starting problems. Moisture could be affecting its operation.
* Ignition Switch: A failing ignition switch might have internal corrosion or wear that's worsened by moisture.
Troubleshooting Steps:
1. Visual Inspection: Thoroughly inspect all wiring and connectors in the ignition system. Look for corrosion, cracks, or any signs of damage.
2. Moisture Testing: Carefully spray suspect areas with a dielectric grease (specifically designed for electrical components, *not* WD-40) to see if this improves starting reliability. This isn't a permanent fix, but helps isolate the problem area.
3. Continuity Testing: Use a multimeter to test the continuity of all wires and components in the ignition system. Look for open circuits or shorts.
4. Check for Arcing: Look for signs of arcing (burn marks) on the wires or components.
5. Professional Diagnosis: If you're not comfortable working with electrical systems, take the vehicle to a qualified mechanic. They have the tools to properly diagnose the problem.
The fact that replacing the distributor cap didn't solve the issue suggests the problem is more widespread within the ignition system itself, and not just a simple cap replacement job. Focusing your investigation on the items above will likely lead to the source of the problem.
