Michigan SOS mechanic test

Heavy-Duty Electrical Systems

Heavy-Duty Electrical Systems is one of the 20 Secretary of State mechanic certification tests. Here's what the test covers, according to the state's published outline.

Topic guide · questions soon

What's on the test

Official topicWeight
System diagnosis
  • Parallel versus series
  • Trailer light diagnosis
  • Relay testing / diagnosis
  • Ground faults
  • Windshield wiper circuit
  • Circuit diagnosis
28%
General
  • Batteries
  • Data bus
  • Welding
  • Module replacement
11%
Vehicle lighting
  • Turn signal circuit
  • Tail lamp circuit
  • Head lamp circuit
  • Trailer wiring
  • Clearance lights
11%
Starting and charging system diagnosis
  • Battery charging
  • Battery load test
  • Alternator output
  • Charging system voltage
  • Circuit resistance
  • Voltage drop test
  • Starter diagnosis
  • Starter draw test
  • Starter terminal identification
36%
Test methods and equipment
  • Voltmeter use
  • Ohmmeter use
  • Circuit testing
  • Diode operation
  • High voltage fuel system
  • Voltage drop test
14%

Source: SOS Mechanic Testing Categories Overview (PDF). Test format: most SOS mechanic tests have 55 questions, and a few have 65–100 (SOS FAQ). Passing scores vary by test; your result letter shows the passing score and your score.

Practice questions coming soon

The Heavy-Duty Electrical Systems practice bank is being written to the official outline below. The All-Mechanic pass will include it when it launches.

Banks available now: Engine Repair · Front End, Suspension & Steering · Brakes & Braking Systems · Electrical Systems · Engine Tune-Up & Performance

Test-day facts

Source: michigan.gov/sos mechanic testing

Heavy-Duty Electrical Systems test FAQ

How many questions are on the Michigan Heavy-Duty Electrical Systems test?

The Secretary of State says most mechanic tests have 55 questions and a few have 65 to 100. The test is “quick pass,” so it ends as soon as you reach the minimum passing score.

What topics are on the Heavy-Duty Electrical Systems test?

The SOS Mechanic Testing Categories Overview lists: System diagnosis (28%), General (11%), Vehicle lighting (11%), Starting and charging system diagnosis (36%), Test methods and equipment (14%).

How much does the test cost, and where do I take it?

Each mechanic test costs $18 (effective July 1, 2026). Tests are taken on a touch-screen kiosk at any Secretary of State office; pre-register and schedule through SOS Online Services. Approved automotive schools can also test their students.

Are these the real test questions?

No. MI Trade Prep questions are original practice items written to the official topic outline. They are not actual exam questions, and MI Trade Prep is not affiliated with the Michigan Department of State.

Sources: SOS mechanic testing · SOS mechanics page · SOS mechanic FAQ