warning light issue
 

Hello, my friend owns an 03 Cayanne Sport and has a warning light issue.
From time to time while driving her interior lights come on and the door open light goes on as well. She is convinced it is the front passenger door. I have inspected it, but am unable to locate some type of switch, which I thought may be shorting out.

Can any one help out with some thoughts on how to proceed? I am sure it could be a simple fix and would like to help her out before she heads into a shop.

Thank you for your time,
Frank