Find the evidence inside the circuit
By the end of this unit, you should be able to identify voltage, current, and resistance; use E = I × R to predict normal operation; choose the appropriate meter mode and connection; and explain how an unwanted resistance or an open changes circuit readings.
Working model: The virtual lab uses a simplified, idealized 12 V DC source, one resistive load, and one connection that can be healthy, resistive, or open. Real vehicle electrical systems can behave differently and require vehicle-specific procedures.
Three different questions, three different measurements
A 12 V battery establishes a potential difference, but that alone does not prove a lamp has a complete path for current. A voltage reading at an open connector may be real even though the lamp remains off.
On a complete circuit, current flows through the load and the source. An open path interrupts that current. A resistive connection can still pass current while wasting part of the source voltage.
Think: What information is still missing?
Reveal the reasoning
No. The voltage indicates a potential difference under the chosen measurement conditions; you must also establish an intact return path and an operating load to infer current flow. An unloaded voltage reading can be misleading.
Ohm's Law tells you what to expect
For an ideal resistive load under steady DC conditions, voltage, current, and resistance are related by:
E = I × R · I = E ÷ R · R = E ÷ ITry one before the virtual lab
A 12 V source powers one 4 Ω resistor. Predict current and load power.
Reveal the reasoning
It decreases in this resistive model. At a fixed applied voltage, I = E ÷ R; a larger denominator produces a smaller current.
A meter is only useful if you connect it correctly
Always note where each test lead is placed. “I measured 12 volts” means very little without identifying the two test points and whether the circuit was operating.
The Challenger asks: Where do you connect a voltmeter to measure the voltage across a lamp?
Place one probe on each lamp terminal while the lamp circuit is energized. Voltage is always a measurement between two points, not a property of a single probe position.
Voltage-drop diagnosis: where is the source voltage going?
Suppose a 12 V source feeds a 6 Ω load through an unwanted 2 Ω connection. The same current passes through the connection and the load.
I = 12 V ÷ (6 Ω + 2 Ω) = 1.5 AThe defective connection wastes voltage while the circuit operates. A voltage-drop test across that connection under load exposes this behavior. A normal healthy connection in our idealized model has essentially 0 V drop.
Now imagine the connection opens completely. Current becomes 0 A. The load drops 0 V in this ideal model, while the open connection can have the full 12 V across it. That does not mean the open connection is successfully carrying current.
Reveal the reasoning
No. The loaded voltage drop across the connector is evidence of unwanted resistance in that connection. A source-side voltage reading alone does not establish how much voltage reaches the operating lamp.
Predict it. Select the meter. Find the fault.
Select a load and circuit condition. Then choose where the simulated meter is connected. The display calculates an idealized DC reading for that test setup.
Healthy loop: the load receives the source voltage and current flows.
The Challenger's lab missions
Complete all four measurement missions by selecting the appropriate circuit condition and meter setup. The mission checklist updates when you make a matching measurement.
- ○Healthy 6 Ω circuit: measure current in series and compare it with 12 ÷ 6.
- ○Resistive 6 Ω circuit: measure voltage across the load.
- ○Resistive 6 Ω circuit: measure voltage across the bad connection.
- ○Open 6 Ω circuit: measure voltage across the open connection.
Reading note: Meter placement is represented by the menu, not by movable probes. This idealized model omits wire resistance, source sag, meter loading, and vehicle-module behavior.
Eight questions. Defend your diagnosis.
Select one answer per question. Your response will be graded with an explanation for each item. You may try again; passing this practice assessment does not certify hands-on competence.
Answer all eight questions, then check your reasoning.
Show it on a real circuit
Use an instructor-approved, current-limited or fused 12 V training circuit with an appropriate resistive load. Have your instructor verify each task before you mark it complete.
What have you demonstrated?
Continue through the lessons and learning activities. Instructor confirmation is required for practical competence.
Progress is saved only in this browser on this device. Changing browser, clearing site data, or opening a differently hosted copy may reset it. These units will be integrated into the main Autonatomy website later.