Why 98 dodge 1500 won't start when it rains?

You need to replace the distributor cap and rotor with factory A/C delco parts. That should fix your problem. You may also need to check the COIL wire at the top of the coil. You can check that by spraying water on the coil with a water bottle and see if it starts. If it don't start then REPLACE the coil and coil wire.