  In this paper we consider the nonlinear equation involving differential forms
on a compact Riemannian manifold $\delta d \xi = f'(<\xi,\xi>)\xi$. This
equation is a generalization of the semilinear Maxwell equations recently
introduced in a paper by Benci and Fortunato. We obtain a multiplicity result
both in the positive mass case (i.e. $f'(t)\geq\epsilon>0$ uniformly) and in
the zero mass case ($f'(t)\geq 0$ and $f'(0)=0$) where a strong convexity
hypothesis on the nonlinearity is assumed.
