Mohammad Samii has operated Sammy's Auto Electric Services in Champaign, Ill., for nearly 45 years. Samii has accrued extraordinary knowledge and experience by performing a wide range of electrical services and repairs.
He diagnoses and repairs nearly every electrical or electronic system on a vehicle. Samii is renowned for solving electrical problems that other auto repair businesses could not.
Besides on-vehicle electrical work, he also rebuilds starters, generators and alternators for auto, truck, marine, agricultural, industrial and aircraft applications. Samii is as comfortable working under the hood as he is toiling at the rebuilder's bench.
He has been presenting electrical seminars to the aftermarket for several decades. Relatively recently, Samii became technical adviser to the Electrical Rebuilders Association (ERA), a trade organization of rebuilders and auto-electric specialists. He also presents seminars on behalf of its members.
Several weeks ago, Samii explained to an ERA conference how fixing a broken tail light became an $800 nightmare.
A local contractor who operates a small fleet of vans brought one to Samii because its right-rear tail light was out. He noticed that an electrical harness connector — the type associated with trailers — protruded from the rear of this vehicle.
Samii quickly collected two vital pieces of vehicle history. For one thing, workers sometimes used these vans to tow machinery-laden trailers to job sites. For another, an employee had wired the trailer's lighting circuit into the van's electrical system.
At some point after the employee made this modification, the van's right-rear tail light went out.
This is where the plot of this mystery thickens. The contractor's vehicle is a 2012 Chevrolet Express Van equipped with a computer network — including a body control module (BCM). Within the last 20 years or so, computer-laden networks have become commonplace on vehicles.
At the risk of over-simplifying the topic, let me contrast newer technology with the old-fashioned gear. For example, a circuit controlled by a conventional switch used to supply battery voltage to a component such as a tail light. Applying voltage to the bulb turned the bulb on.
In bygone days, the switch controlling the circuit was a simple part such as a headlight, brake light or turn-signal switch.
But with the advent of vehicle networks, computers or nodes such as the BCM eliminated many — if not most — traditional switches. The BCM is a brainy box containing myriad solid-state switches. Solid state means that unlike old-fashioned switches, the BCM's switches have no moving parts.
To simplify once again, a transistor or similar electronic component exemplifies a solid-state switch. Typically, transistor-like components are substantially smaller, lighter and more-durable than traditional switches are.
Current, which is measured in amperes (amps), represents electrical volume. Remember that many solid-state components do not tolerate excessive current.
Matter of fact, excessive current may fry an electronic device in a fraction of a second.
Let's return to the Chevrolet Express Van fiasco. The van's BCM senses when the driver turns on the lights, steps on the brake pedal, etc. Then the BCM sends battery voltage to the tail light bulb, turning on the bulb.
A component such as the BCM is designed to carry or handle a specified current — but no more. Excessive amps may destroy the BCM in the blink of an eye.
Remember the electrical connector that Samii found in the rear of the van? The contractor's employee had spliced a wiring harness into the OEM BCM-to-tail light wiring.
This meant that whenever the driver turned on the van's lights or stepped on the brake pedal, the appropriate lights on the trailer also operated.
Unfortunately, the trailer wiring was not protected adequately from flexing and chafing. Eventually, the insulation on one of the wires wore away, allowing bare wire to touch the trailer's frame.
Bare wire touching the frame constitutes a classic — as well as devastating — short to ground.
When the driver turns on the lights or steps on the brake pedal, this short pulls excessive current through the entire circuit, including the BCM.
We can debate and discuss a solid-state device's ability to handle excessive current all day, but the key lesson here was that a shorted wire in the trailer smoked the van's BCM — period.
Samii repaired the exposed wiring on the trailer and replaced the van's BCM. The repair required reprogramming the new BCM. The job totaled $800.