Charging problem

I think you should be looking at the battery connections, especially the supply wires to lights and ignition, check in the harness near the battery. When you first switch on before starting, the charge light earths through the alternator and is fed from the ignition switch so the lamp lights. After starting and the alternator starts to output the lamp goes out because each side of the bulb then has a live feed and nowhere to earth. If you have a difference in voltage on the ignition switch side or the alternator output then the lamp will light again by earthing through the lower voltage. It seems like when the lights are on the battery voltage is dropping gradually until there is a marked difference, enough to stop the rev counter working and light the charge lamp. I think the fault is most likely on the battery to ignition/lights supply. You need to measure the voltages, engine running and lights on, at the battery, alternator output and at the switches end of the supply when the fault occurs. Might get an idea from that, HTH Martin

I my have a solution to this one, Check the fan belt has been fitted round the pullies properly. It is a long belt. This was the problem with mine which had the same problem. The garage that fitted a new water pump got it wrong. I drove the car for months with no problem . Winter comes and the lights are used an the charging problem started.