Oh, damn, the limey's back again...

Something is not right with the total circuit, positive to truck and back to negative post. Did you use a terminal cleaner that brushes post and clamp? Have you cleaned the fusible link connections? They live close to the battery, and are prone to corrode. Also check engine block grounds and the plastic part of the ignition switch.

The loss of radio when the lights go is indicative of a bad connection somewhere, or at least one with high resistance.

I've found the kind of failure you describe is almost always battery terminal corrosion...

Welcome back, Reuben!