Green’s Dictionary of Slang

main drag n.

[main adj. + drag n.1 (1), also note drag (oneself along), to make one’s way wearily, tiredly. The term referred orig. to a town or city’s centre of tramp or vagrant life but was extended and then transferred to the main street, whether or not frequented by vagrants. Despite its almost invariably US use today, the term started in the UK and is cited as such by Mayhew, London Labour & London Poor (1861–2)]

1. [mid-19C+] the main street of a town or city.

2. [1910s–70s] the main road.

3. [1930s–40s] (US black) 7th Avenue in Harlem, New York.

In phrases

buzz the main drag (v.) (also mooch the main drag, work...)

[1920s] to beg along a town’s main street.

main drag of many tears (n.) [the bars and theatres on 125th St (Harlem’s main street) where otherwise depressed and frustrated people can attempt to drown their sorrows]

[1940s] (US black) 125th Street Harlem, New York.