Do you have alternator with external regulator? While car is running, remove positive battery connection, if the car runs then Alternator is good. If the car dies alternator is bad but sounds like if the lights are not working, it may be something else.
Start the engine and measure battery post voltage, should be no less then 13.8 volts.
If less or equal to battery voltage, check the condition of the fusible links, one at positive cable clamp going to junction block and the other link at the horn relay.
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