If the regular bulbs are still in the circuit and not removed, you should not need the resistor since you would be adding to the load, not reducing it. The resistor compensates for the reduced load on the circuit causing the stock flasher to operate too quickly. The improved digital flashers as well as the flashers designed for LED (low load) circuits wouldn't require the resistor.??? If you add LED turn signals in addition to the stock by say splicing into the wires of the existing units, do you still need to add the resistor?