Electrical mystery.....

You don't need an expensive tool to trouble shoot this. A dime store 12V lamp and or an old tail/ stop socket with an 1157, and a meter. YOU ALWAYS need a meter. I just bought three more Flukes off C/L for 25 bucks apiece. They are beaters and they work

Power Probes are not expensive (You dont need the whole kit)and if you ever use one you will know why test lights and multimeters take the back seat.