What is the burden of good cause for a change of plea?

"The burden of showing good cause for the change of plea rests upon the defendant. He should be required to produce evidence which would show the trial judge that there were reasonable grounds to believe that at the time of the commission of the crime he was legally insane and that he was so mentally diseased that he could not distinguish between the right and the wrong of his act or that he was not conscious of its wrongful nature. [Citations.]" (People v. Morgan (1935) 9 Cal.App.2d 612, 615 [50 P.2d 1061].)