Howard,
The 2nd S.C. Cav. was the cavalry component of Hampton's Legion. Capt. Williams' last letter from Wilmington sounds about right. The 2nd was at Fort Fisher in January of 1865. The regiment is listed on the order of battle for the Surrender at Appomattox Court House as part of Brig. Gen. Martin Gary's Brigade in Fitz Lee's Division
Gary's Brigade, Brig. Gen. Martin V. Gary
7th Georgia, Capt. William H. Burroughs
7th South Carolina, Col. Alexander C. Haskell
Hampton (South Carolina) Legion,(2nd S.C.), Lieut. Col. Robert B. Arnold
24th Virginia, Col. William T. Robbins
Hope this helps
Len