S-10 Truck won't start when raining

My 1997 Chevy S-10 truck has a tendency not to turnover when it's raining. I have replaced the distributor cap, wires and sprayed WD-40 and nothing seems to work until it just sits then it will start up on it's own. Any ideas. It always runs somewhat poorly when it is raining sometimes. Any other time no problems.

sounds like something getting wet. have you checked for spark during these conditions? when you changed your cap did it seem damp inside your distributor?

The cap was dry. No dampness. Spark seemed fine. This morning it started and now there is a ticking noise but runs fine.