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?
Tuesday, April 19th, 2016 AT 2:05 PM