What lead did you use to fire the plug with?
If it was the coil-to-distributor lead, then there's a very strong possibility the problem is in the cap or rotor arm.
Check the carbon brush in the centre of the cap and make sure it's present and able to make contact with the rotor arm.
Also check the point of contact where the brush sits on the arm and make sure it's clean.
The module in the distributor is used to create the pulse on the low voltage side of the ignition system without which there wouldn't be a spark.
As the car's electrical system is DC, a pulse is needed to create a rising and falling voltage for the coil, which is really a high-voltage transformer, to step up to the kiovolt=range necessary to cause a spark which won't be extinguished bu the pressure in the cylinder caused by the compression of the air/fuel mixture.
In effect, what I'm saying is that if you have a spark at the coil, any or all of the following components could be preventing it from being transferred to the sparkplugs.
1) The HT lead from the coil to the cap. (If this is providing a spark to the plugs, then rule it out)
2) The distributor cap. Inspect it closely for signs of trackind betwen the electrodes and the centre carbon brush and also between any point and the edge where it sits on the distributor as this could be grounding the spark. These usually appear as a thin black line and is usually a result of carbon residue from the brush sitting in a crack in the cap or following a line of moisture. a crack may not always be easily seen as often it,s only on the surface and not all the way through the cap.
Check externally for signs of tracking between the five £chimneys" where the HT leads attach to the cap and make sure the whole thing is clean and dry.
Also check the centre carbon brush as per above.
3) the rotor arm. Inspect it for wear as described above and also check for continuity between the outer end of the brass contact and the centre point where the carbon brush sits. It needs this path to distribute the HT charge from the coil to each electrode and onto the sparkplug via the HT (plug) lead.
4) the HT (plug) leads. These carry the HC charge to the individual plugs where the gap between the centre tip and the outer electrode creats a path for the voltage to jump thereby creating the required spark. If you found a spark from the coil via the coil-to-distributor lead, substitute it with each plug lead one at a time and see if you get a spark each time.
Finally, the obvious correct gapping of the plugs is essential as the size of the gap determines the quality of the spark.
If the gap is too litle, the spark won't be of sufficient intensity and if the gap is too great, the voltage will fail to jump the space resulting in no spark.
The setting reccomended in your car's manual is the optimum gap required factoring in the HT voltage and the type of plug.
While the whole thing reads like a long list, in reality all the checks can be carried out in a few minutes and if you find the issue early in the process, complete the procedure and check all the components as the few minutes it will take may save you a lot of hardship later.
Now I'm going for a coffee!
