My first guess when you said humidity related was the cap. But since you say you've addressed that, my first thing to do would be use dielectric grease on all connections to seal them
"Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life."
1990 White YJ TBI350, SM465, NP231, SOA, RE 1.5" SOA springs, Ford 8.8, D30, 4.10's, JBConversions SYE, XJ shaft, Bilstein 5150s, jb4x4 steering, MORE SS brakelines, 35x12.50 15 MT's, '95 YJ Brake Booster, '78 Grand Marquis MC, ZJ Prop. Valve