The part I am having a problem with is adding the code to read a pin connected to the flasher relay on the motorcycle and make the led's blink yellow.
What is the voltage on the relay? How are you getting it to a range that the Arduino can handle? In other words, where is your schematic?
if(lsiState == LOW) {
strip_left.show();
I would not expect the relay state to be low to indicate blinking.