If the battery is not recharged, anything can be wrong. It is possible that the battery itself is no longer good, but it is also possible that the alternator no longer wants to charge. In that case, the alternator must be overhauled or replaced. But it is not always what it seems.
What happened to me once is the following. We had traveled to England with an MGBGT from 1975 and returned to Calais in the evening. It was dark and the dynamo stopped. At least it seemed that way. It was decided to wait until it was quiet and then drive home without light. Only when we caught up with other cars was the light switched on and then switched off again. At home the alternator was replaced but the problem was not solved. It was also not the dynamo light and it had to be searched. In the end the problem turned out to be a bad fuse box. A number of brown wires gathered there, including those from the dynamo, and they should make contact there to provide the batteries and the rest of the car with electricity. But the power was from the contacts of the fuse box so that the wires remained in place but no longer made contact. The fuse box was replaced and the problem was solved. This was the fuse box with four fuses from Lucas, which was also used in many other cars. It has the nasty habit of causing many problems. Failing brake lights and direction indicators for example. Or headlights that work on the right and not on the left. Or the problem just described. The box can only be mounted in one way. Because at the rear there is a connection made between the top and the second top fuse. As a result, the headlights and the rear lights should always work together. Pay attention to the correct assembly. Because if the fuse box is mounted upside down, functions have been connected incorrectly that can actually only be activated with the ignition switched on. That is not the intention.
Text and photo: Jacques van den Bergh