General

SIX STEP PROCESS OF ELECTRICAL DIAGNOSIS:
To correctly isolate and repair electrical problems, view the video Electrical Diagnosis (T-9067-1) and follow these six electrical diagnosis steps:

Step 1: Verify the Problem
Review the work order, operate the system, and list symptoms in order to:
^ Check the accuracy and completeness of the complaint.
^ Re-create the problem.

Step 2: Narrow the Choice of Possible Causes of Failure
Refer to the circuit diagram for clues to the problem. Location and identification of circuit components may give some idea of where the problem is.

The circuit diagrams are designed to make it easy to identify common points in circuits. This knowledge can help narrow the problem to a specific area. For example, if several circuits fail at the same time, check for a common power or ground connection. If part of a circuit fails, check the connections between the part that works and the part that does not work.

For example, if the low beam headlamps work, but the high beams and the indicator lamps do not, then voltage and ground paths are good. Since the headlamp dimmer switch is the component which switches this voltage, it is most likely the cause of the failure.

Step 3: Identify the Failed Circuit
Read the circuit operation for the problem circuit identified in the previous step. By studying the circuit diagram and circuit operation, enough information should be learned to narrow the cause to one component or one portion of the circuit.

Step 4: Locate the Failed Component or Element
The diagnosis charts are a step-by-step approach to diagnose a symptom. Each chart covers one symptom. For example, "HORN(S) WILL NOT OPERATE."

The charts are divided into three columns: Test, Result, and Action.
The test procedures are listed in numerical sequence and must be followed in that order. Each test step describes what must be done to the circuit, what test equipment to use and where to connect the test equipment.

After the test procedure has been performed, refer to the result column. This lists possible results of the test. Once the result has been found, follow it directly over to the action column.

The action column instructs what must be done to correct the problem or lists the next test step to be performed.

It is important to remember that a problem in one system could result in a symptom in another system.

Step 5: Make the Repair
Repair the problem circuit as directed in the diagnosis charts.

Step 6: Verify that the Repair is Complete
Operate the system, and check that the repair has removed all symptoms and has not caused any new symptoms.