Adding on/off switch to paneldue

[timcurtis67]

I want to add an on/off switch to my paneldue so it isn't lit up all the time while printing. Which wire is the best to place the switch in? The positive or the negative? Or should I cut both positive and negative?

I'm not sure if any kind of voltage will back feed through the RX or TX wires so that is why I am asking.