Preliminary Testing Procedures

Before testing, obtain Spark Tester (ST-125). See Fig 1 and Fig 2 . If factory tachometer is connected to ignition coil tachometer terminal, disconnect it before performing tests. When performing tests, use digital voltmeter with at least 10-megohm input impedance. When removing spark plug wire from spark plug, twist and pull on boot, NOT on wire.

Fig 1: Integral Coil Spark Tester (ST-125) Hook-Up

Courtesy of GENERAL MOTORS CORP.

Fig 2: External Coil Spark Tester (ST-125) Hook-Up

Courtesy of GENERAL MOTORS CORP.