Before using your wiring diagram, you need to cover the basic wiring checks! If not, you will be wasting a lot of your time and money!


When using any automotive wiring diagram, you need to know how to check the basic wiring rule of car repair: Run a visual inspection on the suspected areas of the problem. This can save you a lot of time and unnecessary parts should you go ahead and start ripping your wiring harness. Remember: most electrical wiring problems do not develop overnight, most of the times it will leave you a clue so you can easily find it.

Let us say one of your headlights is not working and you need to fix it. Using visual inspection, one can do the following basic wiring checks:

Lift up the hood of your engine hood. Go to your headlight seal beam area and check the wires going to the headlight. Checking if the wiring connections are tight and secure can do this. You can also check the harness if it is rubbing on any metal that can cause the insulation to fail. Then with headlights on, try pulling the wires and see if it will make the seal beam light up. Finally, try giving the seal beam itself a light tap and if it lights, you know you got the problem solved.

Other basic wiring check before using your electrical wiring diagram:

Can you see any wire corrosion around the terminal connections? This corrosion is usually greenish in color and is powdery in nature. If you see this, remove the terminal connection and clean it by disconnecting the wire connection and spraying it with a rust penetrant like WD-40.

If you can, see if you can polish the terminals and pins with a sand paper. Once thoroughly cleaned, the terminals can be installed together to check the results. (the best option also is to replace the wiring terminals completely if you have the wiring diagram handy...this way, correct wiring connections are maintained

Have you checked the fuses? Do you know if all fuses are good and not blown? Sometimes it helps to tap the fuse to its terminals to make sure they are not loose.

Using the basic wiring check, you can also trace for any relays present which usually deteriorates when the contacts inside are corroded. This can be easily be checked by tapping the relay and checking if the relay terminals have signs of heat marks and terminal corrosion. Using a test light and the wiring diagram, you can check the relay for source of power and output signal when the relay is activated.

Is the seal beam mounting secure? Are there any signs of rust? Remember that rust will produce poor ground contacts making any electrical device fail.

How does the filament of the seal beam look? If broken for sure means that you need a new part.(and no need to toy around with the wires!).

Have you tested your ground supplies? Using a test light and key on, connect the positive and negative lead of the headlight. If no power on the positive, transfer the ground lead to the vehicle frame or negative battery source. If the positive now lights up, the seal beam is defective whereas if it happens when the seal beam ground connector is connected to the negative lead, your ground connection is bad.

Once you have established that all the basic wiring checks were done to check the physical condition of the electrical wiring problem, then it is about to examine closer your wiring diagram to check the rest of the electrical system.

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