GM went from, in my opinion, the world's second best generator to by far the worst pile starting with the 1987 model year. The failure rate is very high, but that still did not satisfy the engineers. Now they added two not-so-reliable computers to the charging system. System information is calculated by the instrument cluster, then that data is transmitted to the engine computer. The engine computer controls the generator.
I do not have any information on this system's operation, but if the generator works as the diagram suggests, you can try taking some readings on the two smaller wires plugged into the generator. The orange wire is the turn-on signal that tells the voltage regulator to start running the generator. In the past, you would find about two volts on that wire with the ignition switch on and the engine not running. The other ten volts was dropped across the "battery" light on the dash, so that light was on. Once the engine is started and the generator is producing output, the regulator puts fourteen volts back out on that wire to turn the "battery" light off. If you find zero volts on that wire, suspect the engine computer or a break in that wire.
The gray wire is a duty-cycled feed for the generator's field winding. In the past that just had full battery voltage applied to it all the time. It is where the voltage regulator sensed system voltage and it was the supply for the field winding. There is no description to indicate how much this signal affects the generator's performance. To add to the misery, being a duty-cycle signal, it is a stream of voltage pulses that vary between zero and some maximum voltage, typically twelve volts, so it cannot be measured with a digital voltmeter.
Tuesday, February 20th, 2018 AT 7:46 PM