^ First thing I'd be doing is finding out what's wrong with the old fuse box - 14, 15, and 16 should be powered up from the same source, unless the PO cut up the metal rail inside the fuse box when doing the #16 replacement.
Second thing I'd be doing is making sure there's no problems with the equipment which hangs off #14 and #15 and which get power from those fuses.
#14 has the door mirrors, cigar lighter, and radio on it.
#15 has the horn and the windscreen washer pump on it.
(Or, at least, should - one never knows what cowboys have done before, especially given their adversity to documentation).
The (OE) circuit paths for each are in the Green Book, which are very bloody easy to follow compared to Holden wiring books.