1986 GMC Truck

Check for input power at the coil-no power backtrack it to the ignition switch. Power there check out the ignition control module

If no spark occurs, check for the presence of normal battery voltage at the battery (BAT) terminal in the distributor cap. The ignition switch must be in the ON position for this test. Either a voltmeter or a test light may be used for this test. Connect the test light wire to ground and the probe end to the BAT terminal at the distributor. If the light comes on, you have voltage to the distributor. If the light fails to come on, this indicates an open circuit in the ignition primary wiring leading to the distributor. In this case, you will have to check wiring continuity back to the ignition switch using a test light. If there is battery voltage at the BAT terminal, but no spark at the plugs, then the problem lies within the distributor assembly. Pick up coil, module, and/or coil should be tested.

Good luck and let us know. :)

Try this stick a Tach/Dwell meter to the Tach terminal on the distributor, if the needle fluctuates it means the ICM is okay, its closing and opening the primary circuit. Check the coil and cap contact button.

BTW do you have power to the coil.
Note: The ICM is like the Ignition Point Contact it opens and closes the Primary Circuit. The Magnetic P/U and Reluctor is the one that tells the ICM when to do its job.