The ignition on a 1988 and 1989 Chevy GMC is of the conventional style with an external coil and a distributor. The distributor incorporates a hall-effect sensor with the ability to collapse the field in the coil and fire the spark plugs. The coil's primary windings build a high charge of electrical power when fed 12 volts through the coil positive terminal. When the coil's negative terminal is grounded by the distributor, the primary windings in the coil collapse into the secondary windings with enough kilovolts (Kv) to overcome the resistance in the wires and gap at the spark plugs.
Perform a quick test to see why the vehicle will not start. Look at the coil and notice that the plug has two sides. The right side has a pink battery plus (+) and a white (tach) wire. The other side has a white (ignition coil control) and a pink and black (ignition control module) wire. Pull the coil wire out of the distributor cap and lay its exposed end on a good surface, such as the valve cover.
Cut a small piece of insulation off the white wire above the pink and black wire to test the coil to see if it is firing. Connect the jumper wire so it touches the metal inside the wire. Turn on the ignition key and briefly tap the opposite end of the jumper wire to a ground. Every time the jumper wire is touched to a ground, the coil wire should throw a healthy spark if the coil is good. If you can't see a spark, the coil has totally failed. If the vehicle runs poorly and has a misfire, proceed to check for a malfunctioning coil.
Pull the electrical plug out of the coil. Place the voltmeter on the ohms scale. Probe the pink and black terminal with one lead and the coil bracket with the other lead. Resistance should be infinite, which means no continuity or no change in original display. Keep the lead on the pink and black terminal and touch the other end to the white wire on the opposite side under the pink. This is the tach wire. The resistance must be 0.2 to 1.5 ohms or very low. Next, keep the probe on the pink and black terminal and put the probe into the coil tower. The resistance should be 5,000 (5K) to 25,000 (25K) ohms. If the numbers are not within these limits, replace the coil.
