An electrical control system is disclosed for controlling a plurality of variable transmittance windows. The electrical control system comprises a master control circuit and user input circuits for supplying control signals representing transmittance levels for the variable transmission windows, and a plurality of slave window control circuits coupled to the master control circuit, user input circuits and the variable transmittance windows. Each slave window control circuit controls the transmittance of at least one of the variable transmission windows in response to control signals received from the master control circuit and/or user input circuits. Also disclosed are novel methods for the manufacture of an electrochromic device used in variable transmittance windows. Novel structural features for improving heat transfer away from the windows, shielding the window from external loads, and improving the electrical performance of the windows are also disclosed.