Had this problem a year ago in Jan. Had a post titled "Haunted PT"
There is a TSB out for moisture getting into the door and/or hatch key cylinder switches. The problem occured a day after we had a lot of rain/wet snow and the temps dropped into the 20's during the night. Looked out before going to bed to find the interior lights on and the locks going nuts!
dealer replaced the 3 switches under warranty/TSB and the locks have been trouble free since.
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John & Terry - TP's CRUISER - Del Val PT Cruisers
"His"-2002 Inferno Red Touring Edition
"Hers"-2003 Electric Blue Limited Edition