Expert lights stay on

[philok0]

Hi, I have a 98 Expert. The problem is the rear stop and tail, reversing and front side lights stay on all the time with or without key in. The sounder works on opening drivers door, but if I turn lights on full or depress the brake the sounder changes pitch. This fault developed after a week or so of rest suggesting damp/corrosion. How do I disconnect all rear wiring for elimination. I've just about run out of places to look. Any ideas would be much appreciated.