88 Pickup 4x4 4cyl.

This truck wont start first thing in the morning when its been raining or its damp. Its turns over but won't start. A few hours in the sun and it starts right up.

I just had the frame repaired and they took off the gas tank and fuel pump, then put the old pump back on.

Does anyone know how I should start troubleshooting this? Can the fuel pump sending unit assembly get wet and not work ?

 

it was a corroded distributor cap.