^ Thread from 2014......
Regardless, I'll still weigh in. My 99 has the blinker mod done, and I use plug and play LEDs with a standard EP27. I didn't have to do anything fancy.
The blinker mod works by polarity. Incandescent bulbs don't care which way current flows, so no problems. LEDs, by their very nature, do care which way current flows which is where the problems start.
You can get around this using a relay for each side, in theory, but an easier way is to do the blinker mod as normal but to purchase plug and play LEDs which are not polarity sensitive. I'll link the specific bulbs that I have installed. There's really no need to go through a bunch of hassle with boards and modules just to use LEDs.
194 bulb: https://www.superbrightleds.com/more...t-car/199/875/
3157 bulb: https://www.superbrightleds.com/more...-car/917/2265/
I'll even post a clip of the turn signals in action if so desired.