FYI for anyone with the NRC rear LED kit, if you retain the stock front signals your 4-way flashers won't work. My turn signal flash rate (controlled by the ECU) was set to Type 2 when the NRC kit was installed, using the method mentioned elsewhere on this forum. It works great for slowing the signal flash rate back to stock, but I'm guessing the 4-ways use a separate circuit that ignores the 'Type 2' setting, and the different loads of filament bulbs in front and the LED rear cause a sync problem that makes the flashers shut down, which also shorts out my turn signals. Turning the key off and back on resets the system so turn signals work normally, but they short out as soon as I press the 4-way button.
Short-stem LED fronts from the UK are already on the way anyway, and they'll most likely solve this. But I've somehow managed to survive riding 27+ years without 4-way flashers on my bikes, so if they don't work, who cares?!