Wiring problem with LED tails

So I'm putting 4 LED replacement lights meant for a transfer truck on my car. The problem is with the turn signals. The lights have 3 wires coming off them; ground, park, stop/turn. I'm using two of these lights per side and I wired them in parrallel first but the resistance wasn't high enough so the turn signals blink fast. I tried wiring them in series but since there is only one ground for the two circuits in each light they wouldn't work.

Is my only option using resistors to get the resistance I want?

you may have to replace your flasher with a elctronic one.   sounds like the leds dond draw enough to create the correct flash.      XS