Taking the Bull by the Horns with Truck Electrical Circuit Testing

Corrosion increases resistance in the circuit which may lead to improper circuit operation and trouble codes.

Most of us have probably seen video clips of the annual Running of the Bulls in Pamplona, Spain, depicting images of high-strung bulls chasing several adventurous, or even crazy, people down a narrow street. The video typically concludes with the bull hooking some unlucky participant in the backside and pitching the individual up in the air like a rag-doll one or more times.

(Image: Fleet Equipment)

Although I lack the experience of having a bull ram a horn of any of my lower extremities, I have no trouble at all determining that it would be an unwelcome and painful event. Thus, I will never voluntarily take part in the running of the bulls; I just don’t need the bragging rights. At least I have a choice in the matter.

On the other hand, when it comes to inspecting wiring and connectors, I can become the bull. How? By probing, prodding and piercing the connectors and wires.

While it is clearly necessary to check for circuit voltage, open circuits and shorted circuits, there are proper and improper methods to accomplish those tasks. Let’s take a brief look at three improper connector and wire testing methods.

First, simply disconnecting a connector and poking the meter probe into the connector is not advised, as this can spread the connector open to the point of not being able to contact the other connector. Consequently, the test results may be within the specification for the circuit according to the meter; however, the technician just introduced a new problem of an open circuit in the connector.

Another problem with incorrect circuit testing is probing the connector through the connector seals. Circuits often function on very low voltages. The seals built into connectors help to keep out moisture in an effort to avoid corrosion at the connection points.

Such corrosion increases resistance in the circuit which may lead to improper circuit operation and trouble codes. It is a good practice to consult the service information to understand how connections should be disconnected, tested and reconnected.

Lastly, piercing or cutting the wire insulation to test a circuit is never a good idea. Here again, water and other debris can enter in through the exposed wire and cause corrosion and high resistance. Moreover, the exposed wire makes for a potential short to ground point.

Damage to the insulation and related wire damage could necessitate replacing or splicing the wire. When making splices, check the service information for the proper procedure. In some instances, wires may need to be crimped and soldered together to achieve the correct continuity and power flow.

At the end of the day, trying to run with the bulls would not be very helpful for my future well being. That experience is one I will have no problem never entering onto my bucket list. Correctly probing and testing connectors and wires, in contrast, will help make solid professional diagnosis and repairs. That makes for bragging rights worth bragging about.


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About the Author

Jake Schell

Jake Schell is an editorial consultant with Mitchell 1. Previously, he served as Product Manager for the Commercial Vehicle Group from 2002 to 2023. Prior to joining Mitchell 1, Jake spent 20 years as a technician. He holds a Chevrolet Master certification in the transmission category as well as ASE certifications in both cars and trucks.