Checking the coil's HT circuit
If your ignition circuit is giving problems, the cause may lie in the coil's HT circuit. You can make a quick check to find out if this is so.
Disconnect the king lead (the one leading from the centre of the coil to the distributor cap) from the distributor. Use a pair of well-insulated pliers to hold the end of the lead 1/2in (13mm) away from one of the spark plug terminals or the engine block. Remove the distributor cap and make sure the points are closed. Turn the ignition on and with an insulated screwdriver open and close the points.
The spark from the end of the lead should easily jump the gap. If there is no spark, or it can only jump a much shorter distance, the coil is faulty.