How to Master One of the Hardest Parts of the ASE A Series Exam: Electrical/Electronic Systems

Ask a group of technicians which A Series test gave them the most trouble, and A6, Electrical/Electronic Systems, comes up again and again, often alongside A8 Engine Performance.

There are good reasons for that. Electricity is invisible, so you can’t see a high-resistance ground the way you can see a leaking seal. Many questions hinge on reading schematics or interpreting meter readings, and the body electrical section covers everything from power windows to airbags to module networks.

In this guide, we’ll break down what A6 covers, the most important concepts, the traps that catch people, and a focused way to prepare.

What Does A6 Cover?

According to the ASE Automobile and Light Truck Study Guide (2026), A6 has 50 scored questions (plus 10 unscored questions) and a 90-minute time limit, the longest in the A Series. The scored questions break down this way:

  • A. General Electrical/Electronic System Diagnosis (13 questions, 26%): Voltage, voltage drop, current, and resistance testing; waveforms; shorts, grounds, and opens; parasitic draw; fuses, diodes, and circuit protection; schematics; data bus networks; and module replacement and programming.
  • B. Battery and Starting System Diagnosis and Repair (9 questions, 18%): State-of-charge and capacity testing, battery charging, starter current draw, and starter control circuits.
  • C. Charging System Diagnosis and Repair (5 questions, 10%): Voltage and current output tests and charging circuit voltage drop.
  • D. Lighting Systems Diagnosis and Repair (6 questions, 12%): Exterior and interior lighting, headlight aiming and leveling, and turn signal and hazard circuits.
  • E. Body Electrical Systems Diagnosis and Repair (17 questions, 34%): Human machine interface (HMI) systems such as the instrument cluster and infotainment, comfort and convenience accessories, security and anti-theft systems, and safety systems such as supplemental restraints.

Body electrical is the largest single area, but every body question still relies on the diagnostic skills in Area A. Representative tasks include “Check voltages and voltage drops in electrical/electronic circuits; interpret readings and determine needed repairs.”

Core Concepts to Know for A6

Ohm’s Law and Circuit Basics

Almost every A6 question comes back to Ohm’s law: voltage equals current times resistance (E = I x R). Power in watts equals voltage times current (P = E x I). You should be able to rearrange these quickly. For example, a 12-volt circuit drawing 3 amps has 4 ohms of total resistance and uses 36 watts.

In a series circuit, the voltage drops across all the components add up to the source voltage. That’s why unwanted resistance anywhere in a circuit steals voltage from the load. In a parallel circuit, each branch gets full voltage, and total current is the sum of the branch currents.

Voltage Drop Testing

Voltage drop testing is the most important skill on A6. Connect the meter across the part of the circuit you want to check, with the circuit turned on and carrying current. A good wire or connection should show very little voltage. A common rule of thumb is about 0.1 volt or less across a single connection, with slightly more allowed across a full cable or ground path, but always check the manufacturer’s specification.

The key point is that the circuit must be loaded. With no current flowing, even a badly corroded connection shows zero volts dropped across it because no current creates the drop.

Opens, Shorts, and High Resistance

  • Open: A break in the circuit. Nothing works. With the circuit switched on, you read source voltage on the battery side of the open and zero volts past it.
  • Short to ground: Current bypasses the load to ground. On the power side of the load, this usually blows the fuse.
  • Short to voltage: One circuit feeds power into another, so a component may operate when it shouldn’t, or two components may work together.
  • High resistance: The circuit works poorly, such as a dim bulb or a slow motor, because the unwanted resistance drops voltage before it reaches the load.

Battery, Starting, and Charging

  • State of charge: A fully charged 12-volt flooded battery reads about 12.6 volts at rest. About 12.4 volts is roughly 75% charged, and 12.2 volts is about 50%. Remove surface charge before testing.
  • Load testing: A traditional load test applies half the cold-cranking amps (CCA) rating for 15 seconds. Voltage should stay at or above 9.6 volts at about 70°F. Many shops now use conductance testers instead.
  • Starter current draw: High draw with slow cranking points to a dragging starter or a mechanical engine problem. Low draw with slow cranking points to high resistance in the cables or connections.
  • Charging output: Many systems charge at roughly 13.5 to 15 volts, but late-model vehicles often vary charging voltage through the engine or body control module. A reading outside that range isn’t automatically a fault, so check the specification and scan data.
  • Battery replacement on newer vehicles: Many vehicles with battery monitoring or stop-start systems require a battery registration or reset after replacement so the charging strategy matches the new battery.

Parasitic Draw

A parasitic draw test measures how much current the vehicle uses with the key off. Use an ammeter in series or a low-amp clamp, then wait for the modules to go to sleep, which can take anywhere from a few minutes to much longer on some vehicles. Many manufacturers specify roughly 50 milliamps or less, but specs vary. Opening a door or removing the ammeter lead can wake the modules and restart the clock.

Relays, Diodes, and Circuit Protection

On a standard ISO relay, terminals 85 and 86 are the coil, 30 is the power input, 87 is the normally open output, and 87a is the normally closed output. Many relays use a diode or resistor across the coil to suppress voltage spikes when the coil turns off. A fusible link or fuse must always be replaced with the correct rating. Replacing one with plain wire leaves the circuit unprotected.

Network Communication

Modern vehicles share data over networks such as the Controller Area Network (CAN). High-speed CAN typically uses two 120-ohm terminating resistors in parallel, so with the battery disconnected you should measure about 60 ohms between CAN high and CAN low (pins 6 and 14 at the data link connector).

About 120 ohms suggests an open in one branch or a missing terminating resistor, and near 0 ohms suggests CAN high and CAN low are shorted together. Communication problems often set “U” codes and can make several unrelated systems act up at once.

Body Electrical and Safety Systems

  • Supplemental restraint system (SRS): Follow the manufacturer’s disabling procedure and wait time before working near airbag components. Never probe airbag circuits with a test light or ohmmeter.
  • Security and anti-theft: Immobilizer and keyless entry problems often come down to key or fob programming, module communication, or a weak fob battery.

Common A6 Traps

  • Testing an unloaded circuit. A digital multimeter draws almost no current, so it can read full voltage through a corroded connection. Voltage drop must be measured with the circuit operating.
  • Replacing the obvious part. A dim headlight or slow starter is often caused by a bad ground, not the bulb or starter.
  • Mixing up the fuse clue. A blown fuse points to a short to ground. A component that won’t shut off, or that works with the wrong switch, points to a short to voltage.
  • Waking the modules during a draw test. If the reading jumps, something woke up. Let the vehicle go back to sleep before you judge it.
  • Misreading units. 300 milliamps is 0.3 amps, not 3 amps. Watch the meter scale and the decimal point.
  • Missing “EXCEPT.” A6 lists many valid causes, so read EXCEPT items carefully and look for the one that doesn’t fit.

Sample Scenarios

Scenario 1

Consider a question where a vehicle’s left headlight is noticeably dimmer than the right. With the headlights on, the technician measures 12.4 volts at the left headlight’s power terminal and 1.5 volts between the headlight’s ground terminal and the battery negative post.

Technician A says the bulb is faulty. Technician B says there’s excessive resistance in the ground circuit.

The bulb receives nearly full voltage on the feed side, but the ground side drops 1.5 volts, far more than a good ground should. That means Technician B is correct. Cleaning or repairing the ground connection is the right fix, and replacing the bulb would not solve the problem.

Scenario 2

Now consider a question where a customer’s battery goes dead after the car sits for three days. After the modules go to sleep, the technician measures a 400-milliamp parasitic draw.

Technician A says to pull fuses one at a time while watching the ammeter. Technician B says to measure the small voltage drop across each fuse without removing it.

Both techniques can locate the circuit with the draw, so the answer is both A and B. Technician B’s method avoids disturbing circuits and waking modules.

How A6 Connects to Other A Series Tests

A6 skills show up throughout the series, which is why many technicians take it before A8:

  • A8 Engine Performance: Computerized Engine Controls (13 questions) includes DMM testing of voltage, voltage drop, amperage, and resistance, plus sensor waveforms.
  • A7 Heating and Air Conditioning: Operating Systems and Related Controls (19 questions) covers blower motors, actuators, and HVAC control modules.
  • A5 Brakes: Electronic Brake Control (10 questions) relies on wheel speed sensor and module diagnosis.
  • ASE L3: You must pass A6 and A8 before registering for the Light Duty Hybrid/Electric Vehicle Specialist test.

A Focused Study Plan for A6

  1. Week 1: Take an A6 baseline quiz and review Ohm’s law, series and parallel circuits, and voltage drop testing. Practice reading schematics from service information.
  2. Week 2: Work through battery, starting, charging, and parasitic draw diagnosis. Write down the key voltage and current values on a single sheet.
  3. Week 3: Focus on Body Electrical, the largest area, along with network diagnosis, relays, and lighting circuits.
  4. Week 4: Take timed mixed sets and redo every missed question until you can explain why each wrong choice is wrong.

In Pocket Prep, use Build Your Own Quiz to isolate the A6 subject, then use Missed Questions to turn your weak spots into strengths. A Timed Quiz helps you practice pacing for 60 questions in 90 minutes.

Start Preparing for ASE A6 With Pocket Prep

Pocket Prep’s ASE A Series practice questions include 800 questions across A1 through A9, each with a detailed explanation that walks through the reasoning, plus a full-length mock exam for each of the nine tests. Use Level Up to build your electrical knowledge step by step, and set study reminders to keep a daily streak going. With steady practice, A6 can go from your toughest test to one of your strongest.