Trying to Dynamicaly System Clock with Set SYS_CLK_SystemClockSourceSwitch (forrest_erickson)

I am trying to switch from the FRC to an external 8 MHz clock dynamically.I can use the Harmony clock selection Configurator and get my system to run either on the FRC + PLL or the PRIMARYSYS+PLL fine. I have written code to now set one or the other but I..