volvo engine wiring

[Birdseye]

I still dont undertsand it.

There are two wires runing to D+. One of them runs through the ignition bulb, the other through a 33ohm resistance. Between then they provide the voltage to the field coils until the alternator is generating at which time there is then 14.5 volts on an internal connection from the stator to the field coils at D+ and 14.5v at the battery / B+, so there is no voltage difference and the light goes out.

Why two wires? Why not one running though the light?

And what does the black potted thing they call the logic circuit do? Is it, as I suspect, only about running one buzzer from three warning lights?

 

[nigelmercier]

Why two wires? Why not one running though the light?
And what does the black potted thing they call the logic circuit do? Is it, as I suspect, only about running one buzzer from three warning lights?

[1] So it still works if the bulb blows?
[2] See the following:

http://www.ybw.com/forums/showthread.php?406071-DIY-volvo-penta-instrument-panel
http://www.ybw.com/forums/showthread.php?406305-Home-Made-Volvo-Penta-2003-Instrument-Panel
http://www.ybw.com/forums/showthread.php?407283-Volvo-Penta-Alarm-Module-Simpler-fix

 

[Birdseye]

Thanks Nigel - dont know how I managed to miss that correspondence but I did.

Mind you it still doesnt really answer my question. In fact it re-inforces my feeling that the whole set up is far more complicated than it needs to be. I dont have a buzzer in my car or on my bike so whats wrong with wiring up the warning lights to the sensors for oil and water, and wiring the D+ terminal up with the current two wires direct to the on side of the panel switch all without a buzzer? If you were really cautious you could put small 12v relays into the water and oil warning circuits ( arguably the ones which need immediate attention) and use them to activate the buzzer.

What is the function of the zenner diodes and the transistor?