The ammeter was reading backwards, meaning when there was a current draw from headlights the meter would go up towards the positive end and when there should have been a charge from the dynamo/generator the meter would go down towards the negative end. This, among other things, was the cause of much research and pondering to determine if the battery had been installed backwards in the past or if there was some other explanation.
The end of the matter was that the vehicle had probably been correctly converted from positive ground to negative ground, but that the final piece was left undone for some reason and the ammeter wires had not been swapped to read correctly. A relatively simple and quick operation requiring only a flat screwdriver and a bit of care and the ammeter now reads correctly.
Ammeters are not like volt meters, they have to have the full system running through them in order to read correctly, not to mention in the right direction. In the Series 2a positive earth petrol model a heavy brown wire (n) comes from the battery (1) via the starter switch (12) to the ammeter (15) and a heavy brown with white trace (nw) goes to the voltage control box (18) and out to most of the electrics on the vehicle.
Switching the ammeter involves accessing the rear of the instrument panel by removing the three slotted head bolts with captive nuts along the top of the panel and two at the bottom with regular nuts. Then, carefully remembering that the whole system flows through these wires (or preferably disconnecting the battery first), the clips for the in and out wires are removed and replaced in each other’s spots. There is also a smaller brown wire (n) which goes out to the harness and eventually to the dash inspection light sockets (4) which must also be moved along with the heavy brown wire to its opposite connector according to the diagram. Taking care not to disturb any other connections or loosen the warning light sockets from their clips in the panel, the panel is bolted back in place as before and the ammeter now reads as expected.
