Also, maybe check the wires at the ignition switch plug at the base of the column and under the dash. Sometimes the plug and the wires melt and can cause issues. That was what caused my overcharging issue. Blue wire grounding under the dash harness. Mine was on a car not a truck though.
I think I'm getting closer to resolving this issue! At least I've figured out that bypassing the bulkhead fixes the issue!.... I'm about to check under the dash like you said!
