I presume I'm meant to line up 5 symbols between the 2 vertical cables, and flick the switches to correspond left or right. But I'm not sure which symbols I'm supposed to line up here. Is it by colours, is it by matching same symbols, or should there be 5 different symbols?

There are symbols on the wall all around that enclosure.
Each set of symbols controls one of those ropes.
The ropes control the traps below.
You are looking for the symbols that control the trap you want to sabotage.
Once you enter a set of symbols - press the white button and it will show which rope/trap it controls.
Then you set the one that Darren approves of.

I think I checked only 4 sets before Darren gave me the A-ok.

Thanks MaG. Yeah, I'd noticed the symbols around the wall before but since they looked distant and a little hard to make out, I didn't think I'd be expected to actually use them. I got it in two goes and am now going to look for a knife.