I may be tagging in on this thread a little late,but have you checked your ignition wire? (switched 12v source) Sounds like it may be hooked up incorrectly. what radio did you get? factory or aftermarket? brand/model etc??

2000 SVT Black/Tan #1633/2150 (a few mods) Alpine: CDA-9835, MRV-F540, MRD-M550 PG: TANTRUM-X 6.5 COMP all around. Some people wear Superman pajamas. Superman wears Chuck Norris pajamas. CEL currently: Off