Beginning at the Quartz Mountain parking lot, we followed the Chiquito Pass trail north for six miles and crossed the "south fork of the Merced River" (mostly dry at the end of August) to the trail junction at Moraine Meadow. Then we turned and headed east, following the trail toward Fernandez Pass.
Soon the Fernandez Pass trail meets a stream coming down from the north; this is the main part of the south fork of the Merced. Leave the Fernandez Pass trail here and find the use trail that goes upstream -- it is left (northwest) of the stream.
Per Starr's Guide: "A trail goes up the main fork of the stream to Horse Thief Meadow at the headwaters from where Triple Divide Peak and Merced Peak may be easily climbed and marvelous views enjoyed". (That is the only reference to "Horse Thief Meadow" that I have seen; there is no name on the USGS quad maps.)
We enjoyed a fine camp on the bench above (north of) the meadows at about 9600 feet.
From there it is an easy walk into the south-facing bowl formed by Merced Peak and Triple Divide Peak, the ridge connecting them, and their south ridges. The whole south-east side of Merced is ascendable. We chose to wander slabs over toward the low point on the south ridge, then gained the south ridge at the low point and followed it to the summit. This was pleasant: the ridge is solid, as easy as it looks, and pleasant scrambling.
On the return, we just wandered down the not-overly-loose south-east slope.
This is a enjoyable two day trip in late summer. The initial seven miles are fairly dull "in the woods" trail, typical of west-side approaches, but the terrain at and above "Horse Thief Meadow" is fine. Do not do the route early-season: mosquitos are out in force along the Chiquito Pass trail then.