There are lots of potential causes for this sort of behaviour, starting with an alternator that is not working properly or even a body computer that is on the way out. But these symptoms are also a classic indication of a very simple problem; a poor earth somewhere on the car. A modern car has multiple earthing points, and if one is a bit sketchy, it can throw the whole car into chaos. Flickering lights and gauges and warning lights on the dashboard are classic indicators of a bad earth. If that’s the case here, an auto electrician should be able to chase down the fault and fix it permanently.

Unless you’ve been the victim of a cruel twist of fate where something else has gone wrong at the exact moment you fitted the new neutral safety switch, it stands to reason that the new switch is not playing the game. You say you’ve tightened the selector linkage, but did you make sure the new switch was located precisely so that it could detect when the car was not in neutral (and, therefore, prevent it from starting)? By tightening the linkage, you may have moved the trigger for the safety switch to a position where it isn’t allowing the switch to make contact and let the engine crank.

In the meantime, try this: If the engine won’t turn with the gearbox in Park, move the selector to Neutral and see if that changes anything. If the car suddenly starts, you know that the new switch is working but needs adjustment to get it into the correct position.

By buying a manual Focus, you neatly sidestep the biggest problem with this car, that of the perennially faulty DCT transmission. As a rule of thumb, the advice is to never buy a Ford with this transmission, purely because its failure is a question of when, not if.

The irony is that the rest of the car was actually pretty reliable, so as long as the recall for a potential fuel leak caused by a blocked carbon-canister has been attended to, you stand a good chance of buying a reliable car.