My 1997 chevy cheyanne pickup will not start when it rains.

Good advice Jeff, I had a Yamaha that was like this, I finally had to spray the entire electrical system with a silicone based water repellent, that fixed it.

I would suspect bad spark plug wires; they leak worse when damp or wet. Bad coil wire for example, can leak so much that the spark never gets to the distributor.
Generally, I have found that good high voltage (plug/distributor) wiring will even work well with a hose spraying water on them; whereas, bad wiring will cause miss or even a stall.

You can watch the wiring at night and bad wires frequently show up with a glow or spark [stay clear to avoid belts, fans, etc.] I have also run a grounded screwdriver along each wire. However, if one is bad --- replace ALL of them.

Well i tell u that i have had cars and trucks that do this! Why i am not sure . Check and make sure that the seal is around the back part of the hood Is not displaced . (above the distributor) If water is leaking directly on to it that could be your problem! Also make sure the cap is good ! Need more info? So let me know if i can help!! good luck

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/jeff_24365d731679262d