2006 Base Model Convertible: Electrical Issue
I have water in my trunk in the cellophane deposits. I left my top down and covered the car with a semi-water resistant cover. It rained for three days straight. I found both sides soaked with water (driver/passenger). Recently had a brand new radio and speakers installed (Radio powered on with no sound). Brake lights not working (recently replaced brake light switch). Automatic Transmission gear shift locked in park (must use tool to unlock it). Can anyone provide steps to troubleshoot the electrical system to narrow down the issue?

 

Dry the car out and then get into the problems, no point doing much until that happens.

 

Speaking as someone who has done component-level electronics troubleshooting since 1982, NO.

This is one time where logical troubleshooting goes out the window, well, at least, logical troubleshooting is not your first course.
My first move would be to ask my insurance if I am covered for this, if so, hopefully, they will total the car.

Other than that...
Your first step: Disconnect battery NOW. (Water damage is way worse with power applied.)
Second step: Tear the carpet/trim out of the car and dry things out.
Third step: Once things are dry, start looking over connectors and evaluate what the level of corrosion is in the connectors (and later, inside modules, etc.)

Once you get thru those steps, perhaps we can go from there.

 

I doubt that an insurance company will find any compassion in their steely heart to repay you for leaving a car badly protected. They may just raise your premium next time.

 

Search for water in the trunk and for info on the Central Locking Control Module which is probably submerged in water in the lowest part of the trunk on the right side.There are also rubber grommets on the bottom of the trunk that some have slit with a sharp knife to let the water out.