Shop Skills
A question bank tells you whether you knew the answer. It doesn't teach you how the thing works. These do — how a relay actually switches, why a wire can read 12.6 V and still be bad, and what your meter is really telling you.
Every one is free to read, has real spec numbers you can work to, and several come with an interactive trainer you can break on purpose.
17 skills · free, no account needed · part of Overhaul Prep's 12,000-question ASE & EVT prep library.
🔍 Fault-finding practice
Reading about a circuit isn't the same as working one. Take a real symptom, choose where to probe, and call the fault — scored on how few probes it took.
interactiveCircuits & components
How a relay works — and how to test one
The 85/86/30/87 pinout, what each terminal actually does, and the four tests that tell you whether a relay is good in under a minute.
interactiveOhm's law, series and parallel — in the bay, not the classroom
The one formula, plus what actually changes when loads are in series versus parallel — and how to use it to predict a reading before you take it.
interactiveReading a wiring diagram
Symbols, splice and connector callouts, how to trace a circuit from fuse to ground, and what the diagram will never tell you.
Fuses, breakers and fusible links
What each device protects, why a fuse blows again, and why upsizing one is how harnesses catch fire.
Meter skills
Measuring amps without killing your meter
Series versus parallel, when to reach for a clamp instead of leads, and the wiring mistake that blows a fuse inside your DMM.
interactiveVoltage drop testing — the test most techs skip
Why a wire can read 12.6 V and still be bad, and how to find the exact bad inch of a circuit under load.
interactiveDiagnosis
Finding a parasitic draw
How to catch what is killing a battery overnight, why modules need time to sleep, and the fuse-pull sequence that finds the circuit.
interactiveGrounds — why the bad one mimics everything else
How a poor ground produces symptoms that look like a dozen other faults, and how to prove a ground is good rather than assuming it.
CAN bus and multiplexing basics
Why two wires replaced a hundred, what the termination resistors do, and the resistance check that finds most bus faults.
Charging & starting
Battery testing — state of charge versus capacity
Two different questions, two different tests, and why a fully charged battery can still fail the one that matters.
Charging system diagnosis
What the output should be, how to test it under real load, and why the alternator is usually not the problem.
Starter circuit diagnosis
Telling a bad starter from a bad cable, what cranking voltage and draw should be, and reading the click.
Fire apparatus
Fire pump theory - what the panel is really telling you
Centrifugal pump behaviour, why pressure and flow trade against each other, and what the intake and discharge gauges mean together.
Priming, drafting and cavitation
Why a pump will not pull water, what cavitation sounds like, and the lift limits physics imposes no matter how good the pump is.
Aerial hydraulics, stabilizers and interlocks
How the hydraulic circuit holds a ladder up, why interlocks refuse to let you operate, and where to look when a function is slow or dead.