Battery

being 21 years old you won't have to worry about disconnecting the battery because there's next to nothing for computers on 21 year old cars that need power when the car is not running, and if the battery is not very old it won't die on you unless you have something on the car that is defective and is draining the battery....if the little bit of computer things on you car need resetting all you have to do when you reconnect the battery is to turn your key to the on position without the engine starting up for about a few seconds so the battery power is connected to everything and then start the car...my Camaro SS is 23 years old and my present 20 year old Neon have had the batteries disconnected many times over the years and even the radios never lost their station memories unless the disconnects were for a very long time...I suspect the radios will have capacitors that hold enough power to keep the radio station memories for some time and as well even the computers that the older cars have may also have capacitors that hold power for a given amount of time.