We completely determine the
residual automorphic representations coming from the torus of odd orthogonal
groups. Under certain technical assumption on disconnected groups, our results
are valid for symplectic groups and even orthogonal groups. Moeglin has
determined the residual spectrum attached to the trivial character of the
torus for split classical groups. However, non-trivial characters present some
non-trivial difficulties, both local and global. Local problems are resolved in
a companion paper with C. Jantzen, where many other useful results are
obtained.