2000 ram 2500
Okay, got a few problems here.

All of these things happened in the same few weeks.
So, first of all, the tranny speed sensor went out, got that fixed.
Few days later, lost power to radio, mirrors, dome light.
Few days after that, no brake lights or trailer lights.

IOD fuse was blown, replaced it and blew it again.
No power to illumination or cigarette lighter fuse in junction block.
Put a bigger fuse in IOD, it holds until you try to adjust the mirrors.
Thus I believe there must be a short somewhere in the mirrors. Haven't found it yet.
Still don't understand brake lights, unless the IOD powers the fuse connection for those as well.
Any ideas?

 

IOD fuse powers quite a few things. If your truck has a trailer harness, I would start looking at that first. They are notorious for having been very poorly installed. (yeah, crappy work on the assembly line.....)

Welcome to DF!