2001 Mazda b3000 loses power.
 

Got gas one morning before work. Go to start truck and I hear maybe a slight thunk and truck loses all power. No lights no nothing. I check the fuses and the terminals. I take them off to inspect and put them back on. After that power comes back on so I go try to crank it and it loses all power again... please help I checked all fuses except the one under the dash.

My first guess is loose and or dirty connections at the battery

check the connections at both the battery and starter. Both good connections and clean. Will check the ground connection

I agree with the battery issue. Every time I’ve had a loose connection at the battery on my cari will have power to everything like normal and then I turn the key and it all turns off. Then after I stop trying to start the car all power will return. Also less common check to make sure the posts are actually seated in the battery well. I had a friend that had a ram and their truck did the same thing and I checked everything and the terminals were tight. I was stumped. Turns out that the posts screwed into the top of the battery and the positive post backed out a little bit. Probably not applicable but just a thought.