lack of charging system voltage.
Well it maybe that the battery is to small for the truck or the alternator is bad
the fastest way is to disconnect the battery ground wire at the battery for about 10 seconds
The Chevrolet 490 Light Delivery.
The battery symbol light indicates that, for whatever reason, the electrical system in the vehicle is not being supplied with the proper voltage. This is often caused by a malfunctioning battery or alternator. Since the battery is the easiest to remove and replace and is most prone to failure it is recommended that you have the battery checked. This can be done, usually for free, at any auto-parts store.
Try disconnecting battery for about 10 mins. or have vehicle scanned to determine problem or have codes cleared
If it is running on the battery only then that means the alternator is not charging the battery.
the diodes in the alternator have gone
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.
The 1918 Chevrolet 490 Light Delivery chassis cowl was the first truck model Chevrolet built. See the Link Hope This Helps.
A typical corrosive material associated with an automobile, light truck, or SUV is battery acid (sulfuric acid solution in the lead-acid battery).
No in most cases but you do not list model so if it is a large truck it may have two.
altinater is probobly dead