How is the resistor connected into the circuit. Appears to be a resistor used in coil circuit and should have nothing to do with the alternator and is not normally mounted on or near the alternator.
By chance is the #2 wire on the edge plug on the alternator which is cut off on right edge of the picture the same wire that connects back to the right side of the resistor. Where does wire on other side of resistor go? If this side of resistor was connected back to battery source it could drop the voltage at pin 2 causing the sensing circuit in the regulator to see a supposed low battery voltage and increase the voltage output to make up for it.
If this is the case, eliminate the resistor and connect as Janicholson indicates and see if this solves the problem