12V warning light

Question: what is the importance of this warning light and what is its function?

Bubba

You don’t absolutely need the warning lamp. You can substitute an equivalent series resistance or a properly sized and wired diode in place of the lamp.

You can also wire the #1 alternator terminal directly to the ignition switch. However with this arrangement current from the alternator will backfeed the ignition coil after you open the ignition switch making it impossible to shut down the engine.

Personally I prefer the warning light. It’ll tell you immediately if the alternator quits working, a nice feature when others (who don’t understand or don’t check the gages) are using the tractor. The light will also come on should the water pump seize or the fan belt break providing an early warning of an overheat condition.

The light is connected on one side to the field current system inside the alternator and to a switched (12v) side of the ignition. When you turn the key on but have not started the tractor, the field acts as a ground and power flows through the light and then to ground - this lights the bulb. Once you start the tractor, the voltage at the field is powered internally by the output of the alternator. If this value is exactly the same as the battery voltage, then you have the same voltage on each side of the indicator light. If the alternator is charging, the light stays off. If the output of the alternator should drop, there will be less voltage on the field side of the light and more voltage on the switched ignition side of the light. The result is that some amount of electricity will flow through the light and into the field and the light will glow proportional to that voltage difference. Some of the delco alternators also use a resistor in parallel to the indicator light. Hope that helps. I found a good website awhile back about this subject but don't have the address handy.

The answer is, yes.

I had this happen to me once when I removed all the idiot lights from my '74 GMC one ton and added gages. It took a lot of wiring diagram studying before I figured out what was happening. It usually took three or four days to discharge because the current drain is very small.

As the others have said, there must be a diode (which is just a one way switch), a dedicated switch or a light in the circuit.

As long as the circuit is broken (switch turned off) and the light is off, there is no power to the field and no drain on the battery. If the switch is left on, the light will stay lit and the battery will eventually become discharged. We bought a Cub awhile back and it had been converted to 12v alternator with no light but it has a switch. If I forget to turn the switch off, the battery will be dead overnight. Having the indicator light would prevent this problem since the light provides a visual indicator that the switch is still in the "on" position. Don't know if that answers your question but that's all I can say about it.