I've been going through some lights and some of my mini's only half work. I will tap on the ball and then sometimes they come on sometime they don't anyone know what leads them to do this. They are 3 wire commercial mini's
go to holiday light source and get a commercial light testing unit. you use it to find the broken, loose, or burned out mini-light. they run about 135-200 bucks.
plug lights into unit, you isolate the broken circuit on 100's by pulling the 1st bulb of the working 1/2 thus all the lights should be out. you push a button on the light testing unit, and the 50 lights you had the problem with will try to fix themselves. if it is a burned out bulb, it will weld the shunt and make the lights go on. relpace the burned out bulb. if a light is loose or broken, it bill "buzz" the problem socket, and you then replace that bulb. it really is a life saver in my business.