Some possibilities are:
1.Blown or defective fuse (use of a fuse is an aftermarket item)
2.Bad connections at ammeter, or ammeter itself (t0 find out put a jumper wire from one post of the terminal box to the other to take the ammeter out of the circuit temporarily)
3.Bad ignition switch and/or cable, or loose cable connection at switch.
4.Loose or broken wires at bottom of coil
5.Loose or broken wires inside terminal box
6.Loose, bare or broken pigtail wire under distributor plate, or wire grounding to plate or distributor body
7.Points not opening, or point arm grounding to cam due to worn rubbing block
8.Worn electrode in underside of distributor cap
9.Loose or broken high tension wire from coil to cap
10.Condenser burned out or grounding (some condensers are too long and can touch the distributor body inside)
12.Rotor not turning due to loose cam screw or bad timing gear.
Ok now break out a volt meter (a light bulb can give false readings).
Start at the fuse block, you should have voltage on both sides of the fuse. If you only have voltage on one side, replace the fuse of fuse block.
Now with voltage on both sides of the fuse, move up to the junction box. There should be voltage at both terminals. If voltage is present only on one side the problem is at the ampmeter and you should Jumper the ampmeter for now.
You should have voltage on both sides of the coil. If not,
remove the red wire on the coil and check again. If you now have voltage on both sides, you have a problem further on. If the voltage is still only in one side you have a bad coil.
Open the points with a piece of paper and remove the condenser. Turn the key on and you should have voltage at the points.
Replace the condenser and you should still have voltage.
If voltage is missing, remove the top plate and check for voltage on the bottom plate.
Check is the connector from the ignition switch screwed in to far? Do you have voltage on the wire to the upper plate?
Is this wire shorting to ground or broken?