It happens often.

To fix: Tear out the trim in the trunk, all of it. Get to the modules and determine if they got wet. IF so, toss all modules and parts away that got wet and either order new or go to a junk yard and get what you need.

I also tell people to keep in mind that the electrical connectors will be corroded if they got wet. If it happened to me, I'd bring home the last 3-4 feet of the junk car's wiring harness as well. Splice the "new" wiring into your car's harness, throwing away the old corroded connectors and last few feet of wire that was exposed to the water.

You can try various shortcuts, like not replacing the wiring and trying to clean the terminals on the end of the wires (forgetting that the same corrosion has formed between the wires and terminals as has formed between the connector terminals on the module and the end of the wire - you can't clean the contact area under the crimps of the terminals). But, go ahead, try to reuse the old wiring/connectors. It make even work - today. In time, the corrosion will take it's toll and you will be posting more frustrating questions on here...............