What I want to do, is have the Arduino ground that circuit and cut off the power to the LED. I'm only using the LED circuit as an example since if it works with those current hungry buggers then it should work with anything right?
Well there is probably a valid question in there somewhere , but the example is very poor in my opinion.
the actual circuit is a bit more complicated and has a press button switch that grounds the circuit to turn it off (including pulling an IC reset pin low). I need to add an Arduino controlled thing in there to which can ground the circuit in the same way as the switch.