No juice to the amp meter ???
The amp meter is like the FIRST STOP on the electrical pathway, having come from the starter's terminal direct to the amp meter through the terminal.
Disconnect the battery and pop the terminal and instrument panel. Check the amp meter and all connections in that area.
You should also examine the fuse block on the starter if you have one, since they are known to break.
Use a volt meter or test light. You CAN get artificial readings if there is no load on the system, since six volts can be presented by a single strand of wire which will not light a headlight. If everything looks good but you still do not have juice, then test with an ahooga horn or headlight grade bulb to put a load on the system.