• 60 questions

ASE T6 Practice Test

Unofficial truck electrical practice in the five content areas of ASE's T6 test specifications, every answer with its source.

A 12-volt cab circuit has a total resistance of 4 ohms. By Ohm's law, how much current flows?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

Print covers the next 50 questions. Share this set copies a link to the same questions in the same order.

Exam mode: 50 questions, 90 minutes.

More options

Unofficial practice questions, not affiliated with the National Institute for Automotive Service Excellence (ASE). Bank checked October 8, 2026.

Next step Buses too: ASE transit bus practiceASE automobile tests A1 to A8

All 60 questions

General electrical diagnosis 17

  • A 12-volt cab circuit has a total resistance of 4 ohms. By Ohm's law, how much current flows? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-11, Ohm's Law. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • A capacitor is connected from a noisy terminal to ground to suppress interference. What does it do there? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 18, Suppression (capacitors). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • A fuse is found burned. Technician A says a fuse of higher amperage rating should be fitted so that it will not blow again. Technician B says the circuit should be traced and the fault found before the fuse is replaced. Who is right? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Fuses and circuit breakers. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
Show all 60 questions (57 more)

General electrical diagnosis, continued

  • A steady 8-ampere drain is left on a battery rated at 80 ampere-hours. About how long until it is discharged, if nothing recharges it? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 16-2, Lamps (current requirements). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • A vibrating-type circuit breaker in the lighting circuit keeps cycling. By TM 9-8000, how is the shorted circuit located? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 16-8, Overload Breakers. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • How does a zener diode differ from an ordinary diode? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-7, Zener Diodes. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • How is a fuse checked with a test lamp, by the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Fuses and circuit breakers. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • In a series circuit, how does the source voltage compare with the voltage drops across the components? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-12, Circuit Configurations (series circuits). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • Technician A says a transistor can switch a large current using a small current. Technician B says a transistor outlasts the relay it replaces because it has no contact points to burn. Who is right? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-8, Transistors. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • Three 2-ohm lamps are wired in series across a 24-volt supply. What current flows through the string? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-12, Circuit Configurations (series circuits). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • Two heater circuits of unequal resistance are fed in parallel from one fuse. How does the current split? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-12, Circuit Configurations (parallel circuits). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • Two marker lamps are wired in parallel across a 12-volt source. What voltage does each lamp receive? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-12, Circuit Configurations (parallel circuits). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • What does a diode do in a circuit? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-6, Diodes. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • What happens to the resistance of most metal conductors as they get hotter? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 11-10, Resistance. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • Where are fusible links usually found? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Fuses and circuit breakers. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • Which set-up does the Navy manual give before the ammeter is read in a battery drain test? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Battery drain test. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.
  • Why does the Navy manual warn against cutting into a wiring loom or harness during tracing? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Headlights. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area A, General Electrical/Electronic System Diagnosis.

Battery and starting system 13

  • A voltmeter is placed across one connector in the starter insulated circuit of a 12-volt system while the engine cranks. What is the highest reading the Navy manual allows? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Starter insulated circuit resistance test. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • About how much of its 80 °F cranking capacity does a lead-acid battery have at 0 °F? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 12-5, Charge (capacity). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • During a cranking voltage test on a 24-volt system, what is the lowest acceptable reading unless the maker specifies otherwise? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Cranking voltage test. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • Four 12-volt batteries are wired as two series pairs, and the pairs are connected in parallel. What is the result? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 12-11, Battery Installation Configurations. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • The starter ground circuit shows more than 0.2 volt loss while cranking. Technician A says a loose, dirty or corroded connection could be the cause. Technician B says ground cables too small for the current could be the cause. Who is right? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Starter ground circuit resistance test. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • Two 12-volt batteries are connected in series. What does the pair deliver? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 12-11, Battery Installation Configurations. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • Under 49 CFR 393.30, what protects the starting motor cable where it passes through a metal battery compartment? 49 CFR Part 393 (Parts and Accessories Necessary for Safe Operation), section 393.30, Battery installation. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • What does a generator lockout relay do in a starting system? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 14-7, Generator Lockout Relay. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • What is done to the electrolyte level before a battery with vent plugs is put on charge? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 12-5, Charge (electrical action). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • What is the usual result of high resistance in the solenoid switch (control) circuit? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Solenoid switch circuit resistance test. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • Where must the voltmeter clip sit at the battery during a starter ground circuit test? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Starter ground circuit resistance test. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • Why does a maintenance-free battery lose very little water over its life? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 12-8, Maintenance-Free Battery. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.
  • Why must a battery box be ventilated? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 12-10, Battery Installation Considerations. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area B, Battery and Starting System Diagnosis and Repair.

Charging system 8

  • A voltage regulator is set so the system voltage runs well above specification. What is the result? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 13, Regulation of generator output. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area C, Charging System Diagnosis and Repair.
  • Charging voltage is erratic and unstable. Which is a cause listed in the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Excessive output test. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area C, Charging System Diagnosis and Repair.
  • How many diodes are in the rectifier bridge of a typical three-phase alternator? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 13-21, The Basic Alternator. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area C, Charging System Diagnosis and Repair.
  • More than 0.1 volt is read between the alternator ground terminal and the regulator ground terminal under load. What is checked? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Regulator ground circuit resistance test. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area C, Charging System Diagnosis and Repair.
  • On a 12-volt system with the engine running, which dash voltmeter reading is in the normal range given by TM 9-8000? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 17-2, Battery Condition Gages (voltmeter). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area C, Charging System Diagnosis and Repair.
  • The regulator is bypassed and battery voltage is applied to the alternator field. Output is now normal. Where is the fault? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Charging circuit diodes bypass procedure. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area C, Charging System Diagnosis and Repair.
  • Technician A says a shorted diode cuts alternator output more than an open diode does. Technician B says a shorted diode lets current flow back through its winding and oppose the next pulse. Who is right? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Open and shorted diodes. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area C, Charging System Diagnosis and Repair.
  • Which is an advantage of an alternator over a direct current generator? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 13, Comparison to a DC generator. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area C, Charging System Diagnosis and Repair.

Lighting systems 7

  • A truck is 80 inches or more in overall width. What identification lamps does 49 CFR 393.11 require on its front? 49 CFR Part 393 (Parts and Accessories Necessary for Safe Operation), section 393.11, Table 1 (identification lamps, front). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area D, Lighting Systems Diagnosis and Repair.
  • At what brake chamber pressure must the stop lamp switch of an air-braked truck light the stop lamps, under FMVSS 121? 49 CFR 571.121 (FMVSS 121, Air brake systems), S5.1.7, Service brake stop lamp switch. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area D, Lighting Systems Diagnosis and Repair.
  • Both headlights are dim on both beams, and the battery and connections test good. Which other cause does the Navy manual list? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Headlights. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area D, Lighting Systems Diagnosis and Repair.
  • The rear lamps serve as both stop lamps and turn signals. The left stop lamp is dead, the right one works, and the left rear turn signal works. Which part is the likely fault? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 4, Directional signals. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area D, Lighting Systems Diagnosis and Repair.
  • Under 49 CFR 393.19, how must the hazard warning signal unit work? 49 CFR Part 393 (Parts and Accessories Necessary for Safe Operation), section 393.19, Hazard warning signals. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area D, Lighting Systems Diagnosis and Repair.
  • When may a turn signal lamp be optically combined with a stop lamp under 49 CFR 393.22? 49 CFR Part 393 (Parts and Accessories Necessary for Safe Operation), section 393.22, Combination of lighting devices and reflectors. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area D, Lighting Systems Diagnosis and Repair.
  • Which exterior lamps does 49 CFR 393.25(e) let a truck flash, with all others steady-burning? 49 CFR Part 393 (Parts and Accessories Necessary for Safe Operation), section 393.25(e), Lamps to be steady-burning. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Electrical/Electronic Systems (Test T6), content area D, Lighting Systems Diagnosis and Repair.

How this list was compiled: Our own questions, written to the five content areas of the Electrical/Electronic Systems (Test T6) test specifications and task list in the ASE Medium/Heavy Truck Study Guide (copyright 2026, https://ase.com/wp-content/uploads/ASE_MedHeavyTruck_Study_Guide.pdf, linked from https://ase.com/tests/t1-t8/, both opened 2026-10-08), in its shares of 28, 22, 14, 12 and 24 percent. The bank holds 17, 13, 8, 7 and 15 questions in that order. Every fact was read on 2026-10-08 in the public text the question names: 49 CFR Part 393 (lamps, wiring, battery installation, speedometer) and 49 CFR 571.121 (FMVSS 121) at ecfr.gov; US Army TM 9-8000, Principles of Automotive Vehicles (1985); and US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992). The sample questions printed in the study guide were not used. Licence: Questions, choices and explanations are original work of this site.

How it works

This free ASE T6 practice test has 60 truck electrical questions of our own, weighted like the real test. It is unofficial and not affiliated with, endorsed by or sponsored by the National Institute for Automotive Service Excellence (ASE).

Read the full guide

What the T6 test covers

ASE's study guide splits the 50 scored questions: general electrical diagnosis 14, battery and starting 11, charging 7, lighting 6, and related vehicle systems (gauges, warning devices, horn, wipers, accessories) 12. This bank keeps those shares: 17, 13, 8, 7 and 15.

Where the answers come from

Truck lamp, wiring and battery box rules come from 49 CFR Part 393, and air brake gauge, stop lamp and antilock circuits from the federal air brake standard. Circuit laws, meters and test steps come from Army and Navy manuals. They do not cover multiplexed data buses.

Timed or on paper

Exam mode asks 50 questions in 90 minutes, the scored count and time ASE prints for T6.

  • General diagnosis and related systems are 26 of the 50 questions. Be quick with series and parallel circuits before the parts questions.
  • Read voltage drop with current flowing: crank the engine or load the circuit, then measure across one cable, switch or connector.

Questions and answers

How many questions are on the ASE T6 test?

ASE's 2026 study guide lists 60 questions in 90 minutes: 50 scored and 10 research questions that are not counted. You are not told which, so answer every one. The recertification test is 25 questions in 45 minutes.

Is there an ASE T6 practice test free of charge?

Yes. This T6 ASE practice test is free: every question, the timed exam round and the printed paper test, with no account. The questions are our own, not the ones on the real test.

Does T6 count toward Master Medium-Heavy Truck Technician?

Yes. ASE's page says technicians certified in tests T2 through T8 are recognized as Master Medium-Heavy Truck Technicians, and T6 is one of the seven. T1 Gasoline Engines is not required.

Which trucks does the T6 test cover?

ASE's page describes the T series as covering Class 4 through Class 8 trucks and tractors. Its study guide adds that certification needs two years of relevant work experience, and that vocational training may count toward it.

More tests

Show 8 more

Browse Safety and Trades