There seem to have been two small streets called Trotter's Alley. The better-known, which bears that name today, runs west from 2nd Street between Chestnut and Walnut. These are the 1785 listings:
(1785) #1 Trotter's Alley, Bacon, David
(1785) #9 Trotter's Alley, Hynes, Alexander
(1785) #9 Trotter's Alley, Hatcher, John
(1785) Hyns, Alexander, shopkeeper, Trotter's Alley between 2nd and Chestnut
(1785) Thatcher, John, house carpenter, Trotter's Alley between Chestnut and Market
(1785) #10 Trotter's Alley, vacant or residents would not give name
(1785) #11 Trotter's Alley, vacant or residents would not give name
(1785) Chiely, Thomas, potter, Trotter's Alley between 2nd and Chestnut
(1785) Cop, Jacob, wheelwright, Trotter's Alley between 2nd and Chestnut
(1785) Erransatter, Jacob, wheelwright, Trotter's Alley between 2nd and Chestnut
(1785) Esher, George, taylor, Trotter's Alley between Chestnut and Market
(1785) Lacy, Mary, schoolmistress, Trotter's Alley between 2nd and Chestnut
(1785) Miller, Andrew, potter, Trotter's Alley between Chestnut and Market
(1785) Miller, Henry, butcher, Trotter's Alley between Chestnut and Market
(1785) Stult, Adam, cordwainer, Trotter's Alley between Chestnut and Market
The other Trotter's Alley was, according to the 1791 directory, on the west side of Front St. between Arch and Race Streets.
(1791) Bryan, Thomas, cordwainer, Trotter's Alley