Episode 209

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Published on:

5th Nov 2025

Electrical Myth La Resistance! [E209]

Thanks to our Partner, NAPA Autotech Training and Pico Technology

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Matt Fanslow opens with “Resistance is futile” and tackles a common belief: “Resistance always makes current go down.” He walks through why that’s mostly—but not always—true, and shows how electric motors (especially starters) can draw more current when unwanted resistance slows them down by reducing counter-EMF. Along the way he ties Ohm’s Law to real diagnostics, shares a Rust Belt cable-smoker story, and closes with a heartfelt reminder about seeking help for the “stuff” we all carry.

Key Topics

  • The “always/never” trap in electrical claims
  • Ohm’s Law in real life: fixed voltage vs. changing conditions
  • Why motors misbehave: counter-EMF as dynamic “resistance”
  • Starter example: inrush current, RPM drop → current rise
  • High-resistance cables that increase current (and make heat)
  • Where the energy goes: heat in brushes/cables vs. mechanical work
  • Instantaneous truth of Ohm’s Law: accurate at a moment in time, not across changing dynamics
  • Practical tell-tales: slow crank + rising amps + hot/smoking cables
  • Mental health note: removing stigma and getting professional help

Practical Takeaways

  • Motors are dynamic loads. If RPM drops (binding, poor supply, worn pump), counter-EMF falls and current can increase even as “resistance in the circuit” rises.
  • Heat = the clue. Elevated current with slow rotation often means energy’s being dumped as heat (cables glowing, insulation softening, brushes cooking).
  • Measure what matters. Combine voltage drop, current measurement, and temperature/thermal observation under load to find where the power is going.
  • Interpret Ohm’s Law correctly. It holds at an instant; across changing conditions, re-evaluate with the values at that moment.

Case Study Highlight

  • Chevy Suburban (late ’80s/early ’90s): Slow crank, ~400 A draw when ~150 A expected; braided negative cable glows red under a 10–20 s crank. Root cause: high-resistance path + reduced counter-EMF → higher current and wasted power as heat.

Tools & Concepts Mentioned

  • Current probe / ammeter
  • Voltage drop testing
  • Starter relative compression patterns
  • Counter-EMF (a.k.a. back-EMF)
  • Old-school VAT-style analyzer (Snap-on digital variant)

Quotes / Moments

  • “It’s rare we can say always or never.”
  • “Ohm’s Law isn’t broken—it’s instantaneous.”
  • “If it isn’t turning it into work, it’s turning it into heat.”

Thanks to our Partner, NAPA Autotech Training

NAPA Autotech’s team of ASE Master Certified Instructors are conducting over 1,200 classes covering 28 automotive topics. To see a selection, go to napaautotech.com for more details.

Thanks to our Partner, Pico Technology

Are you chasing elusive automotive problems? Pico Technology empowers you to see what's really happening. Their PicoScope oscilloscopes transform your diagnostic capabilities. Pinpoint faults in sensors, wiring, and components with unmatched accuracy. Visit PicoAuto.com and revolutionize your diagnostics today! 

Contact Information

The Automotive Repair Podcast Network: https://automotiverepairpodcastnetwork.com/

Remarkable Results Radio Podcast with Carm Capriotto: Advancing the Aftermarket by Facilitating Wisdom Through Story Telling and Open Discussion. https://remarkableresults.biz/

Diagnosing the Aftermarket A to Z with Matt Fanslow: From Diagnostics to Metallica and Mental Health, Matt Fanslow is Lifting the Hood on Life. https://mattfanslow.captivate.fm/

Business by the Numbers with Hunt Demarest: Understand the Numbers of Your Business with CPA Hunt Demarest. https://huntdemarest.captivate.fm/

The Auto Repair Marketing Podcast with Kim and Brian Walker: Marketing Experts Brian & Kim Walker Work with Shop Owners to Take it to the Next Level. https://autorepairmarketing.captivate.fm/

The Weekly Blitz with Chris Cotton: Weekly Inspiration with Business Coach Chris Cotton from AutoFix - Auto Shop Coaching. https://chriscotton.captivate.fm/

Speak Up! Effective Communication with Craig O'Neill: Develop Interpersonal and Professional Communication Skills when Speaking to Audiences of Any Size. https://craigoneill.captivate.fm/

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About the Podcast

Automotive Field Theory
From Automotive Diagnostics to Metallica and Mental Health
Automotive Field Theory explores the forces that shape automotive repair, including the ones measured with a meter or oscilloscope and the ones that cannot be found on a wiring diagram.

Hosted by automotive diagnostic specialist, shop manager, and instructor Matt Fanslow, the podcast begins in the automotive aftermarket but rarely stays inside its traditional boundaries. Diagnostics, electricity, technology, leadership, psychology, economics, game theory, history, music, movies, family, and human behavior may appear unrelated. Look closely enough, however, and connections begin to emerge.

A vehicle may arrive with a technical fault, but the work surrounding it is rarely technical alone.

Information is incomplete.

People make decisions under pressure and uncertainty. Incentives shape behavior. Standards gradually drift. Good intentions produce unexpected results. The official process may say one thing while the system quietly rewards another.

Automotive Field Theory is an attempt to understand those interactions.

Drawing from real diagnostic work, shop management, industry conversations, personal experience, and an occasionally inconvenient level of curiosity, Matt examines not only how things work, but why they work that way, how they became what they are, and what apparently unrelated subjects might teach us about repairing vehicles, leading people, running businesses, and improving the automotive industry.

Some episodes begin with a failed component. Others begin with Metallica, quantum physics, professional wrestling, a historical disaster, a round of golf, or a question that refuses to leave Matt alone.

Eventually, they all enter the same field.