He's testing switches:
LeftBlinkSwitchState = digitalRead(LeftBlinkSwitch); //reads the switch value
...
////////Start Left Blinker Code//////
if(LeftBlinkSwitchState == HIGH) //if the left blinker switch is on, then...
{
analogWrite(LeftBlink, 225); //starts initial rapid blink
Here's my tentative solution... Use the Crossroads-diode solution for the switches. Have interrupts to determine switch-state changes. In the interrupt routine turn on/off flags indicating which switches are currently down. Have a main loop that blinks things. In the main loop, where you blink/unblink just turn on the things whose corresponding switches are on, and leave off the others. That way they all blink (the ones that are supposed to) and not only that, they blink together (unlike some gadgets I have here).