The control lamp on the instrument panel has two positive contacts, namely, on the one hand, from the terminal «1» generator (white wire) and, on the other hand, from the terminal «A2» ignition lock relay (yellow wire), coming through the multi-pin connection behind the instrument panel.
With the ignition on, voltage is supplied through the yellow wire. The generator is not running yet, so the white wire works like «minus». The warning lamp lights up because there is a voltage difference between the on-board network supplied from the battery and the alternator.
When the engine is started and the generator has reached normal speed, the voltage regulator connects the generator to the on-board electrical network. In this case, the positive charge is supplied through the yellow wire and additionally through the white wire. Now there is no voltage difference and the charging indicator lamp goes out.
When the ignition is turned on, the charging indicator lamp should activate the generator. Thus, it can provide electric current at low speeds. Of course, this is only required when starting the generator for the first time.