Won't start when wet

1995 Chevy Cavalier won't start when it is raining. Engine grinds without starting. If temp drops to freezing - it will start. Problem has also occurred when driving and it is not raining. Engine will quit. If you wait 10 minutes - in dry conditions - the engine will start.
Chevy dealers have no answer.
One local mechanic suggests a new computer for it.
Another suggests a new wiring harness
Ideas of suggestions?

If you have it running when its dark outside take a look under the hood and look for sparks from any part of you secondary ignition,ie plug wires or coil packs.