The passenger doors on the taxi are connected to motion locks – this means the doors are locked from the inside as the car moves, or when the footbrake is depressed.
In theory, this means passengers cannot run off without paying their fare. In practice, you can just wind down the windows and open the door from the outside (as these are just connected to the central locking).
The ‘brainbox’ is the interface between the doors, taximeter, indications on the dashboard and the gearbox. It takes an input from the sense cable connected to the gearbox which gives a small voltage proportional to the speed of the car (hence why it can tell the doors to lock over a certain speed). Likewise, the ‘brainbox’ also sends a signal to the taximeter which relies on distance covered, to calculate a fare. Similarly it has feedback from the small courtesy switches located on the inside of the passenger doors, which beeps and illuminates lights on the dashboard whenever they are opened.
These brainboxes are located below the leaking windscreen, and can therefore fail after a heavy rainfall. I’ve been through 5 of these in the years I’ve had the taxi, costing about £14 each.
Having just purchased a new one for fitting, I will be using bathroom sealant to make sure no more water gets inside…