Backup lights stuck on.

I have a 2002 F250 with a 5.4 V8, I found that the backup lights and taillights were stuck on all night and battery was almost dead. The key was off and the truck in park. There is a slight burnt wire smell in the cab. I pulled the fuse panel cover to check fuses and found oil in the fuse panel and on the lower fuses. It is a clean oil, maybe brake fluid. Could this oil have come from the master cylinder and what could it have done to cause the lights to stay on?
The truck runs and everything appears to function properly but as long as the battery is connected, the lights stay on.