We selected the LittleBits w6 Arduino module in the board manager within the MacOSx version of the Arduino Genuino app. The value for LED_BUILTIN seems to be something other than 5. I haven’t been able to figure out where the define is set. When running the basic blink app, the default code compiles and uploads, but does not blink the lights. When I go and replace the LED_BUILTIN to be a 5, the example works as advertised. Where do the default defines come from in the Arduino compile?
On a regular Arduino board, an LED is connected to pin 13, so any sketch using the builtin LED will assume it to be on pin 13. As you may have discovered, pin 13 is not broken out on the littleBits arduino module. So you can attach the LED to pin 5 or 9 (the ‘bottom’ two output connectors on the module.) So in any sketches you use, be sure to change any reference to an LED on pin 13 to the number of the actual connector you used.