We calculate the broad-band spectrum expected of a 10 exp 7 solar mass black hole accreting from an ambient galactic wind in the nucleus of M31, and we discuss several testable predictions of this model: (1) when resolved, this source will probably be elongated, perhaps in the direction of the semistellar nucleus BD +40 148 deg; (2) its radio spectral index is expected to be about 0.4; (3) the radio component should steepen sharply between about 10 exp 10 and 10 exp 11 Hz; (4) if an association between this radio source and a nearby Einstein X-ray source is confirmed, its radio luminosity should be variable on a time of less than about 1 yr; and (5) the variability of its radio and X-ray fluxes should be anticorrelated.