My old Vectra did it differently.
Across the lamp switch was a high-value resistor. With the switch off, the bulb held its positive terminal low, unless the bulb was blown, in which case the resistor pulled it high.
One drop-off by Vauxhall was the way they used that voltage, at least for the brake lights.
It was connected into the engine-management system, so a faulty brake light gave an engine fault warning.
So you're driving along without a care in the world - until that warning light came on. "STOP NOW BEFORE YOUR ENGINE BURSTS INTO FLAME"
So in panic you press the brake pedal, and the warning light goes off!
It would have been better to have a separate warning light.