'98 chevy express van won't start in the rain

Our '98 chevy express van won’t start when it’s rained recently. After it’s dried out it will start. When it does start initially the gas gauge needle vibrates, but eventually settles down and it steady. Even when it is vibrating is displays the correct anount of gas. I think I have an electrical “short” any ideas where to look first?

Ignition components are the first to look at. Worn, brittle, and cracked plug wires can lead to spark leakage, especially when it is wet out. Same with a worn or cracked distributor cap, if this van still has one.