When changing to LED turnsignals for older 911s and all 914s, the issue you notice is common where one side turnsignals blink as do the other side to a lesser degree. I call this ghosting. Are both L and R indicators in the dash flashing together?
What LED compatible flasher relay was installed? EP26 is pin compatible with the 911/914 but not pin functional as C2 is not powered.
As you noticed the L and R indicators in the tach are wired together on one side and driven by the K/C2 pin of the flasher relay. The flasher relay had a dual use in early 911s and 914s to also flash if the ebrake was pulled or the brake master cylinder fault switch was tripped.
To allow the OEM flasher relay to flash normally (1 flash/sec) with the tiny brake warning light as a load, the OEM flasher would not hyperflash (2 flash/sec) if one of the turnsignal bulbs burned out like most older vehicles would.
Without hyperflash to warn the driver of a burned out turnsignal, Porsche decided to use the L and R indicators to warn the driver of a burnt bulb by flashing together if a bulb is burned. This is why the L indicator is connected to the right side and visa versa. Notice in the diagram below that the flasher relay has a 2nd coil driven by the turnsignal current.
When changing to LEDs, the OEM flasher will sense LED turnsignals as burned out and will not drive K/C2 to 12V. Thus the L and R indicators are just in series and power the opposite side turnsignals.
EP26 is commercially available and is LED compatible although the K/C2 pin is open inside. This pin needs to be grounded to work properly. I resell EP26 with this pin grounded and show how to ground it yourself on my website.
