Q: Truck will crank, but engine won't start - 1973 Chevrolet K20

The old battery in my car would not hold a charge, so I replaced it with a new one. After installing the new battery, the truck will crank, but the engine will not start. I held a plug wire next to ground to test for spark, but there was nothing. I also used the same technique to test the coil wire - nothing. Next, I tested for voltage across the input wires to the coil. When the ignition engaged, there were only 4 volts. Next, at the ignition fuse, in the fuse panel, I tested for voltage and saw 12 volts. I know that from the starter solenoid is the only other direction that the voltage comes from. When I tested there, it was 12 volts going into the solenoid, however only 4 were coming back to the coil. My truck’s starter is a new one that I installed several months ago. Next to the distributor is a small capacitor-looking part in the same bracket with the coil. I don't know if this is a resistor or a capacitor. There is only one connection that goes to the coil’s back side connection. I have been researching for wiring diagrams but so far haven't found any. Could you please give me whatever help you can for these problems?