I teach electrical troubleshooting to technicians, and in the past thirteen years I have come across the same problem time and again:
Manufacturers make it clear--very clear--that using a tool that damages wire insulation is strictly forbidden. These companies spend millions of dollars on R&D to keep water and corrosives out, and your guys still use lighted ice picks to diagnose a $90,000 truck.
There is a way to easily and effectively diagnose electrical system faults without damaging the insulation and wiring, but here's the key: you need a digital voltmeter, you need to understand fault definitions, and you need to know what voltage drop is. Everyone involved with building trucks knows this, but most mechanics are out of the loop on voltage drop. Engineers haven't had an easy way to measure voltage drop so the diagnostics don't call for it. Mechanics have always worked around it, and all have paid the price in unneeded parts and wasted time.
The advantage of reading a voltage drop is that it's a true test of what the circuit can do, and if properly done the reading cannot be confused. The problem is that voltage drops require that nothing be disconnected. However, without opening the connectors, you can't get to the circuit to test it. This is where the supposed true "value" of the sharp tools is seen. If we leave everything connected and poke a hole, the diagnostics concept is better, but the practice badly damages an expensive harness.
All manufacturers want you to use a voltmeter, but they don't account for the flaw that makes their voltmeter measurements incomplete. Do you remember the "NO START" when the diagnostic flowchart asked "Do you read voltage at this point?", and you said "Yes--I do", so they told you to keep going.
This was very bad, right? The fault probably ended up being corrosion six inches from the key switch, but you ended up at the ECM. Two days later you found a green spot in a wire (where someone poked a hole...) that took two minutes to fix after the manual had you replace an expensive ECM. Think about all those transmission faults that ended up being wire problems in the OEM harness.
Herein lies the paradox. What you needed was a way to use ALL of these best practices, without having to accommodate the short-comings with work-arounds. If you could've unplugged the failed component AND read a voltage drop, AND not damaged the wiring with a pick, then you'd have been golden. What you needed was a way to do it all, by having a load built into the voltmeter, that allowed a new voltage drop step to be added simply to the manufacturers' old voltage reading step.
This tool is available, but changing to adopt it will require a wholesale change to the thinking of the industry. Manufacturers will need to change diagnostics because now they can see faults they couldn't before. Fleets will need to adopt a more generous attitude about time management to ensure accurate diagnostics. And, techs will need to start believing they can troubleshoot with a voltmeter.
Making a jury-rigged, "get it running" repair is hard to resist. We all understand the unrelenting tic-toc of the time clock, the NEED to be rolling, the shortage of electrical knowledge, the complex new systems, and bad habits reinforced by "convenient" tools. Don't forget shop ego...
Electrical diagnostics can be simple, if we start looking intensely at the big picture. There are tools that should be used, and tools that shouldn't, and there's no reason that this problem should exist.
What's cheap is expensive, and we need to stop pounding on our left hand with our right.
Voltage drop as a theory and voltage drop testing are often ignored because the test and its usefulness are often misunderstood. Let's clear up that misunderstanding.
Always buy and use the right tools and equipment