Coupe or Roadster? You must inspect the CLP/SSM in the trunk area.

In Roadsters, it's in the passenger side rear wheel well. (Ya gotta yank all the trim from the trunk area.)
In Coupes, it's under the trim on the right side of the cargo area, in back. (Never owned a coupe, but the story is the same; Ya gotta yank all or most of the trim from the area and take a look.)

You are looking for water damage - if you find any, it's time to replace the CLP/SSM with one from a wrecked car (since you can't get them new anymore).

CLP/SSM: Central locking pump/security system module.