Really weird this one.

I recently changed my battery (1 week ago) its been fine and im not sure that it has anything to do with the proble, but the problem is this.......When i get out of the car and lock it the courtesy light dims and the door locks open? I turned off the courtesy lights and this solved the problem.

The problem doesnt stop there. When im in the car and lock the dood internally the locks also open when

- i use the indicators
- i turn on head lights
- i brake
- i turn on heated rear screen
- put car in reverse
- basically anything connected to using lights or light coming on.

The prolem doesnt happen when i use windscreen wipers, heater, radio etc

any thought on that anyone? taking it to a dealer but dont want to get stiched up. Its got to be something? i dont think its the locks that are faulty as they work....any input would be greatly appreciated.