A new calculation of rate coefficients for electron collisional excitation of ion{Fe}{xii} is presented and compared to earlier calculations. Significant differences are found with all earlier work due to the inclusion of resonance processes that have not previously been considered and to the use of the intermediate coupling frame transformation method. The resulting dataset of collision strengths is shown to resolve many of the outstanding discrepancies between theory and solar observations. In particular, density sensitive line ratios in ion{Fe}{xii} now indicate electron densities close to those derived from other ions of comparable ionization potential.