This is very possibly caused by a problem with what’s called the blend door actuator. This – as the name suggests – is a small electric motor that controls the positions of a flap inside the car’s climate-control system that determines how much heat is allowed into the cabin. Over time, the little plastic gears inside the actuator become brittle and break off, and suddenly the door (or flap) doesn’t move, meaning you’re stuck with whatever temperature the climate was set on when the gears broke.

Replacement actuators are available online but before you buy a new one, try this trick which allegedly works sometimes. The problem could be that the actuator is simply out of step with the blend door. At that point, you can try to resynchronise the two and return the climate-control to normal.

To do that, the trade secret is to turn the ignition to on (but don’t start the engine) and then hold down the A/C and Recirc buttons on the dashboard simultaneously. These need to be held down for about 10 seconds, at which point the dashboard lights will flash and the car’s body computer will cycle the actuator to relearn its end points. This process takes a couple of minutes to complete. To be honest, though, it’s far more likely the gears inside the actuator have shattered. But it’s got to be worth a try, especially since it’s free.

A lot of cars have a function whereby the horn will sound when the car is locked if there's a door, bonnet or boot ajar. It's designed to warn the driver that the car may not be fully secure even though it's technically locked.

Sometimes, the little switches that detect whether a door is ajar can become sticky with grit and grime and don't function properly. Locate each switch and give it a quick spray with electrical contact-cleaner and you might find the problem goes away.

If the third brake light is working, then the problem is not with the brake-pedal switch (or the third light would not work either). That the two lower brake lights stopped working together is also a clue that it's not the bulbs that are at fault.

I'd be looking at the fusebox to see if the fuse that controls the lower brake-light circuit has failed. There should be a map of the fusebox inside the plastic cover, and from that, you can identify which fuse protects that circuit, and go from there. If there's no blown fuse at fault, you need to start checking earth connections as these can also cause all sorts of electrical mayhem. An auto electrician could probably sort this quite quickly without changing any more working parts.