I recently purchased a 2000 deville. The service engine soon light came on, the bad thing is that now the lock switches won't work, and my whole instrument panel is going haywire. What could be the ca

Sounds like an electrical problem, maybe simple maybe not. Have you looked under the dash at the fuse panel? might get lucky and find a loose connection. Good Luck

Pull out the rear seat cushion and inspect the mains and accessories fuses, also check the battery cables and grounds, next you should check the harness grounds at both side of the dash panel mounting plate. You may have other problems with engine management and you will have to get the codes for those, use a good scan tool to retrieve them, preferably a scanner that can do live data. Or take it to a shop you trust and have it checked out.