ALT light not working

[L Hud]

The alt light on my 3910 is no longer working. It was working fine, the it stopped. It does not come on at all. I have checked the bulb and the socket. I have power to the socket but no ground. I can ground it to the battery and it will work. I apparently have lost the ground in the system some where. The alt is charging. Have checked voltage at the battery and it is the correct voltage. The light should be on when switched and go out when alt starts to produce volts and removes the ground. Have I lost my ground at the alt. ?? Any help appreciated.

 

[JMOR]

(quoted from post at 08:56:40 02/20/20) The alt light on my 3910 is no longer working. It was working fine, the it stopped. It does not come on at all. I have checked the bulb and the socket. I have power to the socket but no ground. I can ground it to the battery and it will work. I apparently have lost the ground in the system some where. The alt is charging. Have checked voltage at the battery and it is the correct voltage. The light should be on when switched and go out when alt starts to produce volts and removes the ground. Have I lost my ground at the alt. ?? Any help appreciated.

heir is likely an exception out in the world, but I think every brand of alternator that I have ever seen has the charge indicator lamp wired such that ign switch supplies power to one lamp terminal and the alternator/VR supplies power to the other lamp terminal when it is up & running, thus no light as both lamp terminals are at a nominal 12 volts. Then when not up & running the lamp finds a low resistance path to ground via alt/VR and illuminates. So I would be looking at that lamp connection to alt/VR and at that alternator terminal voltage when up & running. Is it same as battery voltage as it should be?

 

[L Hud]

The voltage at the battery is what it should be. I replaced the VR thinking it was not grounding through it. That did not solve the problem. Is there a diode in the alt. that might be out?

 

[JMOR]

(quoted from post at 08:22:08 02/21/20) The voltage at the battery is what it should be. I replaced the VR thinking it was not grounding through it. That did not solve the problem. Is there a diode in the alt. that might be out?

didn't ask about battery voltage. I did ask whether the voltage at alternator terminal feeding lamp was same as battery voltage or not. If not, then diode trio is suspect.