1998 Cadillac Seville Dead Battery

He has what sounds like a parasitic drain on the battery, If it is dying overnight, it is a rather large draw. First question is how much aftermarket(non-stock) equipment is on the vehicle? This comprises a substantial amount of drain issues. Check that neither of the lumbar switches are stuck. Other than that, it can get a bit complex. The draw needs to be measured with an ammeter, and in most cases, the fuses have to be removed one at a time to identify which circuit is draining. From here it becomes a process of elimination. Is it something keeping the data bus alive, or a faulty component. Each power cycle requires a minimum 25 minute power down for true draw readings, it can take some time.