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**VetteVet** · 09-25-2011, 01:07 PM

WARNING LAMP
This is hard to understand but the light does not have a direct path to ground. In other words the light socket is not grounded to the cluster but it has two positive feeds. One comes from the battery via the pink wire from the ignition switch and the other is from the alternator also to the pink wire to the cluster then to the light via the same pink wire but the positive source is different. The brown white wire from the light is the feed path back to the alternator and also the ground path for the light as explained below and by fixit -p.

The alternator warning lamp. As can be seen from figure 5, a schematic for an actual alternator, there is a path to ground from the field current supply input [1] to the regulator. As a result, when the key is turned on, current flows through the warning lamp, through the resisters, transistors, and field coil, and then to ground, causing the lamp to illuminate. Once the alternator is at full output, voltage from the diode trio, also applied to [1], equals the battery voltage. At this time, with 12 volts on both sides, the lamp is out.

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Name: altfig5.jpg
Views: 6288
Size: 61.6 KB

If the alternator should fail, voltage from the diode trio would drop, and once again the lamp would light from the battery voltage. If the alternator output is only a little low, the lamp will be dimly lit. If the alternator fails completely, and the output voltage goes to zero, the lamp will be lit at full brilliance. Conversely, if the battery should fail, and the battery voltage drops, with the output voltage of the alternator on one side and the low battery voltage on the other, the lamp will also light.

As stated earlier, if the light grows dimmer as the engine is revved up, it is because the alternator voltage is rising with the RPM, producing more voltage on the alternator side of the lamp. The closer the output voltage gets to the battery voltage, the dimmer the bulb becomes. By the same way, if the light gets brighter with increasing RPM, it is because as the alternator voltage increases, it is getting higher than the battery voltage. The higher the voltage with respect to the battery voltage, the greater the voltage difference across the lamp, and the brighter it gets.

If you look at the diagram I posted In my last post it shows the wires going to the light and the return paths to the ignition switch and to the alternator.

DISCLAIMER: I believe that this is the way it works so if I am wrong then some one please correct me. VV

09-25-2011, 01:07 PM	#16
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,723	Re: 67-72 not charging...WHY? WARNING LAMP This is hard to understand but the light does not have a direct path to ground. In other words the light socket is not grounded to the cluster but it has two positive feeds. One comes from the battery via the pink wire from the ignition switch and the other is from the alternator also to the pink wire to the cluster then to the light via the same pink wire but the positive source is different. The brown white wire from the light is the feed path back to the alternator and also the ground path for the light as explained below and by fixit -p. The alternator warning lamp. As can be seen from figure 5, a schematic for an actual alternator, there is a path to ground from the field current supply input [1] to the regulator. As a result, when the key is turned on, current flows through the warning lamp, through the resisters, transistors, and field coil, and then to ground, causing the lamp to illuminate. Once the alternator is at full output, voltage from the diode trio, also applied to [1], equals the battery voltage. At this time, with 12 volts on both sides, the lamp is out. If the alternator should fail, voltage from the diode trio would drop, and once again the lamp would light from the battery voltage. If the alternator output is only a little low, the lamp will be dimly lit. If the alternator fails completely, and the output voltage goes to zero, the lamp will be lit at full brilliance. Conversely, if the battery should fail, and the battery voltage drops, with the output voltage of the alternator on one side and the low battery voltage on the other, the lamp will also light. As stated earlier, if the light grows dimmer as the engine is revved up, it is because the alternator voltage is rising with the RPM, producing more voltage on the alternator side of the lamp. The closer the output voltage gets to the battery voltage, the dimmer the bulb becomes. By the same way, if the light gets brighter with increasing RPM, it is because as the alternator voltage increases, it is getting higher than the battery voltage. The higher the voltage with respect to the battery voltage, the greater the voltage difference across the lamp, and the brighter it gets. If you look at the diagram I posted In my last post it shows the wires going to the light and the return paths to the ignition switch and to the alternator. DISCLAIMER: I believe that this is the way it works so if I am wrong then some one please correct me. VV __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.