I hate to state the obvious but you have a direct short or loose wire somewhere. My first step would be to make sure the connections on the battery are clean and tight. I have also had problems with the body ground wires. These could be corroded, loose or broken. Sad to say it could be anything from a loose/broken wire to a blown fuse when dealing with electrical issues. Good luck check starter cylinoid on inside fender wall.
try replacing the alternator
They do. Did you ever stop to consider that there might be something wrong with your vehicle and not all 1988 BMW's? Guess not.
if you didnt un-connect the battery you could have fried it.
In the 1988 Nissan the alternator, instrument panel, and backup lights shared a fuse. Before changing a fuse see if the backup lights work (have someone watch when you are in reverse). If the neutral start/backup light switch is broken internally, it can be blowing the fuse when you put the car in reverse.
Do you mean What does it mean when the brake and battery lights come on in when it is already started? Check your alternator may be its not working well it cause the battery sign comes out.
Sounds like a bad battery cable connection or a dead battery
It is possibley your alternator or battery
Possibly a bad alternator (the system is not charging the battery).
All the warning lights are supposed to turn on for a few seconds as a "bulb check" when turning the key to start the car. Do the lights stay on after the car has started? If so, you could have anything from a faulty ground to a damaged computer.
Try looking at your fusible link that is connected to the battery, if it is 'blown' you will not get power to anything.
your battery is dead