Hello, I am interested in installing LED running boards on my 2016 Mercedes GLE450 AMG Coupe. Can you please provide guidance on which wire to tap into so that the lights on the running boards turn on when I use the unlock function on the key fob and the headlights are on? What color is the relevant wire?

You need to tap into the wire for the parking lights. In your car, that wire is most likely the brown wire with a red stripe.
Test it with a multimeter first to be sure. When you unlock the car or turn on the headlights, that wire should show 12 volts.

Thank you but where is the wire inside of the car?