What causes the BCS and the TCS lights to lite up on the instrument panel some of the time on 99 Olds sillhoute.

Have you been having performance issues, where the CEL comes on? Those lights often come on when the ignition system is compromised. How long has it been since you changed spark plugs, Ignition Control Module, and coil packs?

You will need a scan tool to retrieve the codes that have set.
Get those and let us know.