What do you mean by four-way flashing? I don't think my winkers do that.
when you install led's into all four winker assemblies and hit the turn signal it will almost act as if it is a four way flasher. This is due to the low current that is traceling through the indicator bulb on the dash. To stop the flow of electricity from backfeeding into the dash bulb, I installed a resistor.
This gentleman can explain it better than I can.