Testing the ignition coil on your 1998 GMC truck will tell you right away if the coil is faulty. Learning the procedure for testing the coil can save time and money. The coil on the GMC looks a little different from the older cylindrical coils that previously sat on these engines, though the function is the same. You will need a digital multimeter to test the coil; if you don’t have one they are available at home centers and auto parts stores.
Disconnect the negative battery cable from the battery after loosening the retaining bolt on the cable end with a wrench. Isolate the cable from the battery, which eliminates any chance of the ignition becoming energized while you are working on it.