Apparently modern cars do not use a flasher relay, the body computer controls the indicator flashing. You'll need to put resistors in each indicator bulb circuit.
But he said they're LED, that means they don't have enough wattage for the flasher controller to flash them at the right speed. So they need resistors, no?
Also, installing the correct wattage resistors results in the power being dissipated in a form of heat, so the leds will draw the same ammount of power as the bulbs... So if you installed leds to save power, then it was superfluous. Same for sidelights.