i have no power to the cab of my 95 nissan truck will not start checked fuses and also main relay under hood all fine im stumped

I just had the same thing happen in my '97 Nissan. It was my boneheaded fault. My battery died and I connected jumper cables backward to jump start it. It was only for a couple seconds, but apparently it was enough to fry a conduit and everything went pffft. No stereo. No speedometer, odometer. No brake lights, turn signals, AC. The only things that worked were the headlights and the wipers. I did the same check of all the fuses and relays and nothing seemed wrong there. My mechanic found what he called a "Fuseable Link" that was a $6 part that he had to solder in place and everything's back to normal.