Specify options for the bar and plot legends. Using different LEGEND statements and positioning the legends in different places for the bar chart and the overlay plots causes GBARLINE to produce two separate legends instead of combining the legends into one.

/* Bar legend */
legend1 position=(middle right outside)  across=1
        label=(position=(top )  j=l "Customer Sector");
/* Line plot legend */
legend2 position=(bottom right outside) across=1 repeat=1
        label=(position=(top) j=l  "Generation Source") ;