This is just an informational post and a thanks to all the members of this board who pointed me in the right direction.
I have a 94 F250 with a 460 and E4OD. When I bought the truck the fuse for the dash illumination was blown. It had a 20 amp in it and the fuse chart called for a 15. So I put a new 15 in it. Everything went fine during the daylight hours (mostly) sometimes the truck would feel like it shifted into neutral, but this didn't happen often.
When I turned the lights on at night or early in the morning on the way to work, the dash lights would stay on for a few minutes, then blow the fuse and the transmission would really start to slip out of gear.
I started looking for answers and got a wiring diagram for the truck. It confused me even more, because the dash lights and the transmisson had nothing to do with each other. Still looking for answers I found this website and did a search on transmissions shifting into neutral.
Presto, I learned about the Manual Gear Lever Positon Switch. I took mine out and tested with an ohm meter according to the Ford Factory Service manual. The maximum resistance was 466 ohms, and mine read 480 ohms. That was enough to make the transmission shift into neutral while driving. I experimented by exchanging switches with my wifes 94 Bronco. The Bronco started doing the same slippy/neutral shifting as the truck did. I replaced the switch with a new one from the ford dealer, I could have ordered one from AutoZone, but it would take a couple of days and I was impatient.
That solved both the dashboard illumination and the shifting problems.
I hope this essay helps someone else avoid a transmisson rebuild, cause that's what the local shop recommended to me
Leroy

 

I am still confused as to how your dash lights come into this??
My trans. does the exact same thing, and I already had that sensor replaced.

 

The only theory that I can come up with is that the manual lever sensor also shares a common ground and with the switch being worn out, it used the path of least resistance back through the gauge illumination circuit. It worked like that until you turned the lights on, then it shorted the circuit to ground and blew the fuse (every time).
It's just too much of a coincidence to believe the two are not related because when I replaced the manual gear sensor two weeks ago, the gauge illumination fuse hasn't blown.
fuse has been fine.
Or it could be EFM (electrical f***ing magic):-)
Leroy:-)

 

EFM......VERY TECHNICAL TERM I LIKE IT!