My battery doesn't last overnight

Hello I had an issue about a drain in my car, fully battery dies in one night. I did a check with my multimeter to know where it came frome. I pulled every fuse out and the problem excisted. When I pulled my cable from my alternator out the drain stopped. I already did buy a new battery and my alternator whas also changed 2 months ago. I checked if my new alternator did his job right with charging my battery and it does correctly but still when the engine is off it drains my battery. My question is could it be a fault in the rectifier diode of my alternator. Please help because I cant find anything about this