Electric field measurements during 28 magnetopause crossings by the ISEE-1 satellite within 2 hours of local dusk in 1980 are examined for the presence of dusk-to-dawn electric fields just inside the magnetopause, since such fields are proposed to be produced by a viscous interaction or other processes occurring in a closed magnetosphere. Although dusk-to-dawn fields containing few kV potentials were often observed, it is concluded that less than 10% of the typical magnetospheric electric potential resulted from the viscous interaction or similar processes.