I used 2 wires to the side marker, one is groud on the turn signal the other is power, I turned the turn signal on & tapped the wires, to see which ones blink at the same pace as turn signal. thats how I did it, not sure about fast blink. A fast blink is usually caused by a burt bulb or bulb of different rating in the circuit make sure all bulbs in the circuit are same brand & wattage.

Hope this helps