2000 F-450:Fuse problems

This is my son's account. My 2000 F450 powerstroke diesel with auto transmission, blew the ecm/gauges fuse (position 19) when I pushed the O/D off button on the end of the gear shift about two months ago when I was pulling my 35 foot 5th wheel camper down a mountain. All the gauges went dead and the motor just idled but did not die. I then shut off the motor and restarted it and it ran fine but still no gauges. About an hour later I finally figured out it was a blown fuse. I replaced it and it worked fine. I did not push the O/D off button until about 2 weeks ago and after about 5 times it blew the fuse. The gauges went did but it still had power. I am in California and I live in Kansas so I thought I would have the dealer in Kansas check it out when I get home next week.
Tonight, my son pushed the O/D button accidently and it blew the fuse. This time the engine would idle only. No response when he would step on the accelerator. We replaced the fuse and it worked fine until we put it in reverse. The fuse would blow again. Every time we put it in reverse now the fuse blows. It works fine if we replace the fuse, start the truck in neutral, then put it in drive.
One other symptom, the reverse lights have not been working for about a month. The truck always has a trailer hooked up to it so I did not worry about fixing them. I did wash under the back of the truck (flatbed) this morning. I didn't have any problems until my son pushed the O/D button tonight and now putting it in reverse kills the fuse every time. I will check the wiring to the reverse lights tomorrow. I suspect blown bulbs, but thought I could be the missing piece to the puzzle.
The truck has 97,760 miles and I believe the ECM is warranted with the powerstroke until 100K.
Any suggestions please?

You have got to have shorts in your wires some where.

check the o/d wiring at the end of shift leveron top of calumn