Most Likely Culprits:
* Ignition System: Water leaking into the distributor cap (if equipped) or ignition coil could cause intermittent starting problems. The water interferes with the electrical connections, leading to a failure to spark the plugs.
* Wiring Harness: Water intrusion into the engine compartment's wiring harness is a major possibility. Look for areas where water could pool and damage the insulation on wires, causing shorts or open circuits. Pay close attention to areas near the firewall, under the hood, and around the windshield.
* Sensors: Various sensors (crankshaft position sensor, camshaft position sensor, etc.) are sensitive to moisture. Water can short them out, preventing the engine from starting.
* Computer (PCM): While less likely due to its location, a severe leak could reach the Powertrain Control Module (PCM). Water damage to this is serious and usually requires professional repair.
* Starter: While less common for rain-related issues, a faulty starter solenoid could be intermittently affected by moisture.
Troubleshooting Steps:
1. Visual Inspection: Thoroughly examine the engine compartment after a rain. Look for obvious signs of water intrusion, wet wires, or corrosion. Pay particular attention to the areas mentioned above.
2. Check the Distributor Cap (if equipped): If your Windstar has a distributor, inspect the cap and rotor for signs of moisture or corrosion. Replace if necessary.
3. Follow Wiring Harnesses: Carefully trace the main wiring harnesses to look for any damaged insulation or signs of water ingress.
4. Sensor Checks: If you have a multimeter, you can test individual sensors for proper resistance and voltage. Consult a repair manual for specific testing procedures for your vehicle's sensors.
5. Professional Help: If you're not comfortable inspecting the wiring or testing components, a qualified mechanic is the best option. They have the tools and expertise to diagnose the problem accurately.
Important Notes:
* Safety First: Disconnect the negative battery terminal before performing any electrical checks to avoid accidental shocks.
* Repair Manual: A repair manual specific to your 1999 Ford Windstar will be incredibly helpful in identifying component locations and testing procedures.
* Don't Drive It: Continuing to drive the vehicle with a known electrical problem could worsen the damage and create safety hazards.
Finding the source of the water leak is just as important as fixing the electrical problem. Otherwise, the problem will likely recur. Look for leaks around seals, windows, and anywhere else water might enter the engine compartment.
