Deliberate mistake: 9/6/10: When Lucas and Jade are getting into the car, look at the road sign behind them. Lucas is driving down a one way street the wrong way. Also the camera light is reflected in the side of the car.
Deliberate mistake: 21/10/08: Jack was giving Darren a driving lesson. Just after Tanya and Lauren got into the back seat of the car, the camera angle changed. As Darren turned the corner into Bridge Street, the driver of the car changed, as he was now much bigger than Darren.
Answer: Most likely a mistake by the set designers or it's a recycled set which already had the switch on (they just repaint and add other fittings).
At my workplace there is a two-gang switch with a three-gang switch underneath it, one of which is for the shop lights, the other four have no apparent use.