I live in a old home half house is wired old other half new well I wanted to know if in the old box if one of the main fuses is blown out will stuff still work because in my son's room half the room works and the other half does not I have checked and replaced the little screw in fuses and have have also checkled the new box and everything is good so could it be one of the big main fuses .. sorry if it sounds funny

I'm installing GFCI outlets in a 2 wire system at home, replacing 2 prong outlets. I'm currently installing Legrand 0026603 self test model. Also bought a Southwire 40020S Receptacle Tester with GFCI test function. I installed the first GFCI a few days ago and believe the R.T. tripped the GFCI that day. Today I installed a 2nd Legrand and the R.T. would not trip the outlet. I tried it on the first one I installed and it would not trip it either. So I tried it on another older GFCI that was already in the house and it tripped that one. The test and reset function works properly on both Legrands. So what should I think about that? These GFCI outlets have been interesting to work with. Fyi the wiring is circa 1945 and nearly all outlets have a single drop except this 2nd one which is connected to a light switch. I am only connecting to the line side and have verified hot and neutral (w/ meter). Also can this R.T. tell if H and N are reversed if there isnt a ground?