no spark on 86 cavalier

no spark at plugs. too the elect moduel out of the distributor and Auto Zone said it was o.k. I bought a external coil and installed. Car ran 1 minute and no spark. Took the coil back to "Auto Zone and got another. Car ran 30 minutes and no spark. Coil has good ground. AZ said there is no way to test this coil. I am thinking now of removing the small magnet/coil from the distributor rotor shaft and replacing it. Question is, it plugs into the elect moduel with 2 wires. If i measure continuity with an ohm meter will it register for the coil magnet? is this a good test? im thinking the magnet/coil is bad? i cant hardly believe the main coil assembly (external) has failed 3 times? must be something else. any ideas?

First, which engine do you have? 4 or 6 cylinder? Second, I wave the BS flag about not being able to test the coil. If you have a distributor, then you definitely can test it. The coil should have 3 connections, one for the coil to distributor spark plug wire, one for battery power and one for the module. The two smaller connectors usually are marked with a "+" or a "-" although it really doesnt matter. Those two connectors make up the primary winding in the coil, a resistance measurement between the two should be between .3 ohms and 1.0 ohm subtracting the resistance of the test leads. The secondary circuit is tested by a resistance check between the coil wire terminal and one of the first two(doesn't matter). The resistance should be like somewhere between 20K and 30K ohms if I remember, but you should check a Haynes or Chiltons for proper values. As for the Magnetic pickup in the base of the distributor, a resistance check is all that is needed there also. Again check the manual for details on the resistance value. There is one other item you may have a problem with. Your Electronic Spark Control Module. Some 80's GM's have it, some dont. Yours may be faulty. The ESC modifies the advance of the timing from other engine sensors. If the ESC is faulty, that would definitely cause a intermittant fault. Hope this leads you to a solution. But nothing substitutes a shop manual. -Chris