  We present dilepton spectra from p+p, d+p and p+Nb reactions at SIS energies,
which were simulated with the GiBUU transport model in a resonance model
approach. These spectra are compared to the data published by the HADES and DLS
collaborations. It is shown that the $\rho$ spectral function includes
non-trivial effects already in elementary reactions, due to production via
baryon resonances, which can yield large contributions to the dilepton
spectrum. Dilepton spectra from nuclear reactions in the energy range of the
HADES experiment are thus found to be sensitive also to properties of nucleon
resonances in the nuclear medium.
