No Ammeter Reading - Would You Scrub?

[cowman]

My answer for something of this nature is it depends. I checked out the airspace around OP's airport and with no way of verifying you have a working charging system and not needing to get home I think I would have done the same.

OTOH I have departed knowing I have a charging system problem. In that case I wasn't in a terribly busy area, was far from home, weather was clear, and I was going directly to an airport where I could get repairs done.

 

[MajorTurbulence]

The KC-135 won't have the same system so many small airplanes use. In most airplanes that don't have an ACU (Alternator Control Unit, the electronic doodad that unifies the regulator and overvolt circuitry), that alternator light simply tells you whether the regulator is switched on or not. The overvolt sensor is in the line between the ALT switch and the "S" terminal of the regulator, and if it senses an overvolt condition it shuts the regulator off (which shuts the alternator off) until you recycle the switch. The alternator belt could fail, or the gear drive, or the output cable or field wire could fall off the alternator, and that light will not illuminate. The alternator could fall right out of the airplane and it wouldn't light up. The light is fired by an internal source in the regulator that has nothing to do with alternator output. These older regulators were adapted from car systems, but the car was wired differently so that the light illuminated if the alternator quit. The airplane is wired so that the system can be shut off, and that function was sacrificed in the process.

Switching the ALT switch off just tells you the light is working, and not much else. Pilots that aren't mechanics with some detailed knowledge of the system won't know that. It's easy to get complacent though ignorance.

This makes sense given my past experience with alternator failure in my PA28-181.
I was flying practice approaches with a CFI on board at night when we got slight squealing noises in the headset with load meter zero, but the idiot Alt light did not light up( or IIRC, maybe the most faint lit and questionable indication in the dark). We were not sure what was going on but headed back to home airport not far away. I never trusted that idiot light alone for alternator failure, and thus got a voltage indicator going forward. Your explanation now makes it clear why that happened.