Gen idiot light help

[Karzapart55]

My 72 bus gen light glowed very slightly when running. at idle had 12.6 at the battery. I thought it was a poor ground at the dash socket. removed the wire, took a small lamp with jumpers, one to blue wire one side to ground. No light. I took a temp wire from reg to idiot light still nothing Any ideas?

[busdaddy]

The charge light doesn't "ground" anywhere, both the wire from the regulator (blue) and the insulated metal area the bulb holder snaps into (black #15) are positive power, when one wire makes more or less voltage then the other the bulb lights. A glowing light indicates weak connections somewhere between the back of the bus and the front, often more than just one.
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[Karzapart55]

Thanks Bus Daddy, its starting to make sense. so if I put a test lead from 15 on the coil to one leg on the blue wire from reg it should work?

[busdaddy]

If you put a test light between #15 and the blue wire it should light when stopped and go out when running, don't put power directly to the regulator. Or a light between the blue wire and ground should light when running, but remember the alternator requires the backfeed of voltage through the bulb to supply the exitement to begin charging so start with the ground clip of the test light on some positive source of power.
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[telford dorr]

X2

Tests: measure the voltage between the regulator D+ terminal and battery "+", and (using a long wire) between battery "+" and the 12 volt black feeder to the idiot lights mounting plate. Both should be zero. One of them won't be. Clean, wiggle, and tighten connections between the alternator/regulator, starter, and the front of the bus. One or more connections need help. Sometimes it's caused by a failing ignition switch.

Explanation: the ALT/GEN idiot light assumes the buss voltage at the front of the bus is exactly the same as at the battery. If not (e.g., there's a voltage drop in the path), the ALT/GEN light will glow slightly.
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[Karzapart55]

I ran a new blue 16ga wire from the regulator to the dash. I hooked up a test light between the blue wire and the fuse feeding ignition terminal 15. Have bright light with ign on, but glows slightly when running, and no rise in voltage at batt. How can I test alt? I also tried with 2 different regulators, no difference

[telford dorr]

[Karzapart55]

Thanks, I'll try that tomorrow Had enough today, gonna go watch the Giants!

[Karzapart55]

Thanks to all who helped. It was the ring terminal on the alt. to starter wire. It was tight , but oxidized inside. replaced terminal, cleaned all starter connection, and im back in business Thanks again