Easy way to tell 12awg from 14awg metal clad?
Take a piece of #12 scrap wire and compare it to what you have. If the wire is the same it is 12, If the wire is larger usually #10 if smaller #14 other than an electric range # 14,12 &amp; 10 will be everything except  the range it will be much larger. These are the sizes used in a 1940’s era homes for the most part.