To plot anything as Candlestick, you need at least two values (high & low).
So Advance Decline would be something like this. Notice that I am repeating a and d twice when passing to PlotOHLC.
Code:
a = AdvIssues() ;
d = DecIssues() ;
PlotOHLC(a,a,d,d, "A D Candle", colorDefault, styleCandle | styleOwnScale);