The alternator light circuit is different from the charging part. The charging part goes to the battery, while the light part goes to the instrument panel. There seems to be a grounded wire in the light circuit.
Inside the alternator.
Well it maybe that the battery is to small for the truck or the alternator is bad
The Chevrolet 490 Light Delivery.
If it is running on the battery only then that means the alternator is not charging the battery.
Very likely an alternator problem; if the alt is not working soon the battery would be drained and the truck would shut off.
the diodes in the alternator have gone
The 1918 Chevrolet 490 Light Delivery chassis cowl was the first truck model Chevrolet built. See the Link Hope This Helps.
the starter,battery and the alternator are good,icheck and change the the wires but the light inside the dashboard,the headlights come on but the truck will not start.
If the alternator belt is tight, the alternator may be at fault.
The alternator has a serious failure.
You probably have a bad alternator. Need to check the charging system.
Disconnect the battery. Remove the air inlet tube. On some s10s, there is a bracket above the alternator that needs to be removed. Take off the serpentine belt. Remove the alternator wiring, then the bolts. Remove the alternator and install the new one.