Then you should have something "in the car" headlights, etc
Reach up and wiggle the ammeter connections with the headlight switch on. Any difference?
Make sure the red ammeter wire does not go dead with lights turned on. If so this might indicate a fail right in the red wire at the bulkhead connector or the fuse link.
The circuit path is starter relay..............fuse link..........(red) bulkhead.......... (red) ammeter..........black ammeter ............TO THE WELDED SPLICE in the black ammeter...............to the (black) bulkhead..........to the alternator
WELDED SPLICE branches off and feeds
fuse panel "hot" buss
headlight switch power for headlights only (not tail or dash)