Hi Grumpy_Mike,
Thanks for your response. I've been doing a bit of digging these last few days but it's not clear to me how their could be a ground wire missing given that there are no wires involved in my circuit:
Arduino -> DMX Shield -> PAR can LED
In similar set ups to mine online it doesn't seem like anyone is doing additional wiring...Could it be that either my DMX Shield or Arduino is faulty? Or that I need to install a ground wire somehow?
Thank-you!