Ignition Coil Primary Circuit Switching

1. Place ignition switch in "OFF" position. Disconnect wiring harness connector from ignition module. Inspect connector for dirt, corrosion and damage. Repair if necessary. If okay, reconnect harness. Connect a non-powered 12-volt test light between coil "TACH" terminal and engine ground. See Fig 1.
2. Crank engine and observe test light. If test light comes on or flashes, remove test light. Proceed to IGNITION COIL PRIMARY RESISTANCE test.
3. If test light does not light or if it is very dim, remove test light. Proceed to PRIMARY CIRCUIT CONTINUITY  test.

Fig 1: Ignition Coil Primary Circuit Switching Test

Courtesy of FORD MOTOR CO.