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  Diagnostic Aids  


These six steps present an orderly method of troubleshooting.

Step 1. Verify the concern.

  • Operate the complete system to check the accuracy and completeness of the customer's complaint.

Step 2. Narrow the concern.

  • Using the wiring diagrams, narrow down the possible causes and locations of the concern to pinpoint the exact cause.
  • Read the description notes at the components and study the wiring schematic. You should then know enough about the circuit operation to determine where to check for the trouble.

Step 3. Test the suspected cause.

  • Use electrical test procedures to find the specific cause of the symptoms.
  • The component location reference bars and the pictures will help you find components. Component location information for connectors, diodes, resistors, splices and grounds can be found at Vehicle Locations.

Step 4. Verify the cause.

  • Confirm that you have found the correct cause by connecting jumper wires and/or temporarily installing a known good component and operating the circuit.

Step 5. Make the repair.

  • Repair or replace the inoperative component.

Step 6. Verify the repair.

  • Operate the system as in Step 1 and check that your repair has removed all symptoms without creating any new symptoms.

Some engine circuits may need special test equipment and special procedures. See Testing and Inspection for the specific component, system, or sub-system in question.

NOTE: Most Ford testing and inspection procedures will be found at the system/sub-system level; only a few component tests are provided by OE.


This is a test lead used to connect two points of a circuit. A Jumper Wire can bypass an open to complete a circuit.

WARNING: Never use a jumper wire across loads (motors,etc.) connected between hot and ground. This direct battery short may cause injury or fire.

A DC Voltmeter measures circuit voltage. Connect negative (- or black) lead to ground, and positive (+ or red) lead to voltage measuring point.



An Ohmmeter shows the resistance between two connected points.



A Test Light is a 12-volt bulb with two test leads.
Uses: Voltage Check, Short Check.



The Self-Powered Test Lamp is a bulb, battery and set of test leads wired in series. When connected to two points of a continuous circuit, the bulb glows.
Uses: Continuity Check, Ground Check.

CAUTION: When using a self -powered test lamp or ohmmeter; be sure power is off in circuit during testing. Hot circuits can cause equipment damage and false readings.

In an inoperative circuit with a switch in series with the load, jumper the terminals of the switch to power the load. If jumpering the terminals powers the circuit, the switch is inoperative.

(Locating open circuits)
Connect one lead of Self-Powered Test Lamp or Ohmmeter to each end of circuit. Lamp will glow if circuit is closed. Switches and fuses can be checked in the same way.



Connect one lead of test lamp to a known good ground or the negative (-) battery terminal. Test for voltage by touching the other lead to the test point. Bulb goes on when the test point has voltage.



A fuse that repeatedly blows is usually caused by a short to ground. It's important to be able to locate such a short quickly.

  1. Turn off everything powered through the fuse.
  2. Disconnect other loads powered through the fuse:
    • Motors: disconnect motor connector (Connector C4).
    • Lights: remove bulbs.
  1. Turn Ignition Switch to RUN (if necessary) to power fuse.
  2. Connect one Test Lamp lead to hot end of blown fuse. Connect other lead to ground. Bulb should glow, showing power to fuse. This step is just a check to be sure you have power to the circuit)
  3. Disconnect the test lamp lead that is connected to ground, and reconnect it to the load side of the fuse at the connector of the disconnected component. (Connect the test lamp lead to connector C4).
    • If the Test Lamp is off, the short is in the disconnected component.
    • If the Test Lamp goes on, the short is in the wiring. You must find the short by disconnecting the circuit connectors, one at a time, until the Test Lamp goes out. For example, with a ground at X, the bulb goes out when C1 or C2 is disconnected, but not after disconnecting C3. This means the short is between C2 and C3.



Turn on power to the circuit. Perform a Voltage Check between the suspected inoperative ground and the frame. Any indicated voltage means that the ground is inoperative.

Turn off power to the circuit. Connect one lead of a Self-Powered Test Lamp or Ohmmeter to the wire in question and the other lead to a known ground. If the bulb glows, the circuit ground is OK.

These diagrams make it easy to identify common points in circuits. This knowledge can help narrow the concern to a specific area. For example, if several circuits fail at the same time, check for a common power or ground connection (see Power and Ground Distribution Diagrams). If part of a circuit fails, check the connections between the part that works and the part that doesn't work.

For example, if the lo beam headlamps work, but the high beams and the indicator lamp don't work, then power and ground paths must be good. Since the dimmer switch is the component that switches this power to the high beam lights and indicator, it is most likely the cause of failure.


The following illustrations are known examples of wiring harness, splices and connectors that will create intermittent electrical concerns. The concerns are hidden and can only be discovered by a physical evaluation as shown in each illustration.

NOTE: Several components, such as the PCM, utilize gold plated terminals in their connections to the wiring harness. If those terminals need to be replaced, they must be replaced with a gold plated terminal.