1987 Chevy Van startering

First thing when its moist outside is to pop the hood and take off the distributor cap, check the rotor, the pickupcoil and cap for moisture, dry them off and try to start it, it run now?

With the engine running on a hot dry day, preferable somewhere dark as in a grage with the lights off. Set parking brake, block all wheels and put on service brake, put vehicle in 1st gear and work it through 0 to up to 2000 rpm, then try second then drive. Do you see any sparks showing up?

Another thing to do is get a bottle of salt water in a spray bottle and spray the electrical components, if the engine hesitates when you spray in one area or you see th electricity arcing in the air, you found the problem