Checking these are very easy if you have a multimeter. There are two systems fitted to these, Lucas and Bosch, the latter being more common but the checking procedures are identical.
1. Connect your voltmeter red lead to the positive side of the coil and the black lead to battery negative. Switch on the ignition and you should see around 12v. Crrank the engine to make sure you still have 12v on cranking. If you don't you'll need to establish why you have no feed to the coil, but you could confirm this by using a jump wire from battery + to coil + and then see if the engine starts.
2. If the above is ok connect your red lead to coil negative. Make sure the coil is still connected and crank the engine. You are now checking to see if the coil is switching. This is where it will be a little bit confusing so I will try to explain. The coil switches on and off four times per rotation, and so it will switch from 12v to 0v continously as the engine turns. A digital multimeter cannot react to this change fast enough to keep up with it, and so if the coil is switching you should be reading either a fluctuating voltage or it will settle somewhere between 12v and 0v. A meter with duty cycle would be the best type to use but I am assuming you don't have one. You could also use a test lamp which if was was flashing would indicate the coil is switching, and if it's on continuous would indicate it isn't switching.
3. If you've established that the the coil is not switching then the ignition module is most likely the cause. Remove the ignition module from the side of the distributor body. You will see two pins coming up from inside the distributor. These come from the inductive pickup. These rarely fail but to check it connect your multimeter leads to each of the two pins. Set the meter to Ohms and you should read between 150 and 1500 Ohms. Then switch your meter to AC volts and crank the engine. You should read upwards of 0.5v AC while cranking.
If this is ok and the coil is not switching then the module is faulty and needs to be replaced. Make sure you smear some heat insulating compound on the back of the new module which is usually supplied. If you don't your new module will fail prematurely. Hope it helps.
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