Chrysler LHS electrical issues

Kinser1970

Working on my friends 1999 LHS. Needed to change the battery so I brought it to my house to sit over night and work on in the morning. In the morning, when I was going out to work on the car, I heard a loud clicking noise coming from the car. Found the interior door lights were on (they were off the night before) and the headlight relays were clicking and the battery was completely dead. Tested the battery and it is bad. Talked to my friend and she said that if the light switch it not switched to off, the interior door lights will come on and drain the battery down. I am thinking she may have a short in the light switch. Any suggestions on properly diagnosing with out just throwing parts at it. The heater control lights don't work either so you can't see if you have the A/C on or the heat what not.