Parallel electric fields can exist in the magnetic mirror geometry of auroral field lines if they conform to the quasi-neutral equilibrium solutions first suggested by Alfv¿n and by Persson. Such solutions may contain double-layer discontinuities, reflecting the disparity between the two sources that contribute to their plasma population-the hot and rarefield magnetosphere, magnetically confined, and the cool dense ionosphere, held down by gravity. This study reviews previous results on quasi-neutral equilibria and on double layers and then examines the effects on such equilibria due to nonunique solutions, potential barriers, and field-aligned current flows, using as inputs monoenergetic isotropic distribution functions. Among the conclusions reached are the following: (1) Double layer solutions not involving any net current flow are readily constructed; (2) Such layers may occur naturally and may involve a significant fraction of the total field aligned voltage drop; (3) Nonuniqueness of quasi-neutral solutions must be utilized to determine the position of such layers; (4) The gravitational potential barrier that confront escaping ions plays an important role and must be taken into account; (5) Outbound field-aligned currents are carried primarily by precipitating electrons and only a very small fraction of them is due to ionospheric positive ions; ((6) Inbound field-aligned currents require an appreciable voltage to drive them, and their density is no greater than that of outbound currents; (7) Precipitation with no net j∥ sets up a 'thermoelectric potential' similar to the one predicted by Hultqvist. Overall, the model suggests that quasi-neutral equilibria can explain many of the observed features of field-aligned currents and of their associated electric fields, though solutions at this stage do not extend to voltage exceeding 2.2 kV.