  We find that the zero mode($q^{+}=0$ mode of a continuum theory) contribution
is crucial to obtain the correct values of the light-front current $J^{-}$ in
the Drell-Yan($q^{+}=0$) frame. In the exactly solvable model of
(1+1)-dimensional scalar field theory interacting with gauge fields, we
quantify the zero mode contribution and observe that the zero mode effects are
very large for the light meson form factors even though they are substantially
reduced for the heavy meson cases.
