1999 Cadillac STS car dead

You may have a simple, common generator failure. Charge the battery for an hour, then measure it's voltage. Start the engine, then measure the voltage again with the engine running and holler back with those numbers.

Follow the smaller battery wires to where they connect and be sure those connections are clean and tight. The negative wire will bolt to the body. The positive wire will typically bolt to the under-hood fuse box. Look if there's another fat wire coming off the fuse box and be sure that is tight.

You can also use a test light starting at the battery and working your way down the cables to the next accessible points to see where the voltage is lost. The first place you lose the voltage is the point of the bad connection. For this to be more accurate it is best to turn on the headlights or something else to try to draw some current even if they aren't working.

Don't overlook blown fuses too. When you disconnect the battery to charge it or to replace it very often fuses blow from the current surge when you reconnect it.