what is the dimmest star in the constellation Andromeda?
S Andromedae is 2.6 million light years away, and was the dimmest star, it actually was a supernova in 1885 with a magnitude that peaked at 6, but dropped to 16 by 1879, its iron core was last seen in 1995 with Hubble. So the dimmest you can see without an observatory would be Ross 248 or HH Andromedae which is a flare star which means its luminosity changes from time to time, but it has an apparent magnitude of 12.29.
