I have a 1999 Ford Ranger 4X4 which continually blows fuse #27. This fuse controls the back-up lights, overdrive, vacum hub locks. Sometimes it will blow a new fuse immediately, and sometimes it may be hours before it will blow. There is no set pattern that causes it to blow. I disconnected my trailer wire harness but it still blows. All the wiring for the trailer and back-up lights appear to be in good shape. If anybody has had this problem or may have a solution, please let me know.

 

I would look at the splice's for the trailer harness.