when it rains water leaks into the trunk

Trunk water leaks on a 1999 Cadillac Seville are commonly caused by a worn trunk lid seal or poor sealing of the tail light assembly. The best way to diagnose the fault is to remove the contents and trim lining from the trunk, climb inside with a flashlight, close the lid and have someone spray water on the outside. When you see the water coming in you will know the cause of your leak.