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This is an incredibly common problem and is usually traced back to a badly wired or damaged plug that joins the electrical systems of the car and the trailer. In fact, there are two halves to this plug, one which is permanently wired into the car, and the second part which is attached to the trailer and plugs into the car. Either half can give trouble.

Over time, these plugs and their wiring can become worn and damaged and the wires loosened, at which point the lights on the trailer won’t work properly. You may even find that the plug on your trailer is wired incorrectly for the car, leading to some of the lights working and others not.

An auto electrician should be able to sort this quickly and inexpensively.

This can happen and it makes a diagnosis very difficult. What you really need to do is find an expert on this make and model. The chances are they’ve seen this very problem on more than one occasion and will be able to quickly pinpoint the cause and a fix.

Some cars can have a misfire (which could conceivably prompt a shift to limp mode) but because the problem is not something that the computer controls, no fault code will be logged. A good example are the spark plugs in some late-model Holden V8s.

In this case, a spark plug that fails can cause all sorts of running problems, but because the spark plugs are not monitored by the ECU, no fault code shows up. That’s when an experienced mechanic will make the connection and replace the spark plugs. That’s the sort of workshop you need to find.

It’s very possible that the continuous clicking noise you can hear is the central locking trying to lock the vehicle but, for some reason, not achieving the desired result. That could be because there’s a misalignment between the bits that actually physically do the locking. If these aren’t aligned correctly, they can’t physically interlock and lock the vehicle. And when that happens, they keep trying which causes the continuous noise you’re hearing.

But the cause could also be a problem with the car’s body computer. This computer is responsible for all sorts of tasks including the stereo, air-conditioning, wipers, lights and, of course, the central locking. If the computer loses the plot it can easily convince itself that the car is unlocked and needs to be locked. Over and over again.

However, the body computer also takes its cues from a variety of sensors around the car, including little switches in the central locking to tell it that the car is locked or unlocked. If one of these fails you could get similar symptoms.

But before any of that – and it sounds pretty basic – walk around the car and make sure all the doors, windows and engine cover are closed properly, as a slightly open window or ajar door will often confuse a central locking system.