Had a dead battery

You blew a fuse. You should have found dozens of blown fuses. All computer modules have a diode in them to prevent damage from reverse polarity. Diodes are one-way valves for electrical current flow. They are in the circuit backward so they are turned off and no current flows through them. When the polarity is reversed, they turn on and act like a short circuit which will make fuses blow. That prevents damage to the rest of the circuitry.

DIFFERENT GUY

START METHODICALLY CHECKING YOUR FUSES

REPLACE THE BLOWN ONES WITH THE SAME "AMP" FUSE

THERE MAY BE MULTIPLE FUSE BOXES (UNDER HOOD/ INSIDE)

WHEN YOU GET DONE

SEE WHAT WORKS AND WHAT DON'T

REPORT BACK HERE WITH YOUR FINDINGS

THE MEDIC

Check the fuses. There will be at least two for the radio, but they may not be labelled as such. The radio's memory circuit is always tied in with some other circuit that is always live. The interior lights is the most common, but the cigarette lighter, horn, and brake lights are other common possibilities.

To make the job easier, every spade-type fuse has two tiny holes on top where you can poke the probe of a test light. Turn the ignition switch on, then probe both sides of each fuse in the fuse box inside the vehicle. If you find voltage on both sides of a fuse, that one is good and that circuit is currently turned on. If you find 0 volts on both sides, that circuit is turned off and doesn't apply to the radio. You're looking for a fuse that has 12 volts on one side and 0 volts on the other side. By testing this way, a mechanic can check every fuse in less than a minute without even wasting time trying to figure out which fuse is the right one to check.

If you don't find a blown fuse inside, there is another fuse box under the hood. Many of those fuses can be checked the same way, but the larger ones are checked visually. You aren't likely to find a blown fuse there unless a number of circuits are dead. Those fuses feed many other circuits that have their own smaller fuses.

Have you determined why the battery was dead?