Lesson Plan Industry Sector
Transportation

## Test Lights (updated) by Michael Fleming

### Lesson Plan Overview / Details

Students will learn how to properly use a test light to check for power and grounds.

### Lesson Time

Two 60 Minute Days
2 Days

### Objectives and Goals

• Students will understand the basic construction of a series circuit.
• Students will identify how circuits require power and grounds.
• Students will understand the use of a test light to check for power and ground.
• Students will use test lights to check for power at the fuses and for continuity at grounds.

### Activities in this Lesson

• In the front of the classroom, set up a rollaway tool chest with a battery pack placed on top. Have a test light nearby and a portable light bulb curcuit comprising of three bulbs hooked in series.  When students come in, have them open their notebooks to a blank page. Instruct them to take notes on all classroom instruction.

1st - Show the light board hooked up to the battery pack with all three lights turned on. (A light board can be three tail lamp bulbs hooked up in series.) Ask the students what are the essential things necessary for a circuit to work. List them all on the board making a star for power and ground. Use of a red plus symbol and black negative symbol next to the words positive and negative is preferred.

2nd - Transfer the battery pack to the rollaway tool chest. Reinforce color and symbols by holding up the battery cables. Explain that you are now going to make the chest ground by connecting the ground cable to it.

3rd - Bring out the test light and ask if anyone knows or can describe the tool (i.e. clip, cable, light bulb, metal "poking" tip). Explain that this tool can be used to test power and grounds in a circuit.

4th - Reinforce that the chest is now ground, and to test power, the test light must be hooked up to ground. The metal tip now can be used to touch the power cable. If their is power the test light will illuminate.

5th - Reinforce color and symbols of negative and positive. Then hook up the test light to the positive side of the battery pack. Then (with the battery ground still hooked up to the chest) proceed to poke through the paint on the chest so that the test light illuminates. Poke the test light all over the chest and call on students to explain why the test light illuminates. Write suggestion / answers on the board.

Safety: Explain that to apply power to ground without any load is a short. A short will "let the smoke out" of the circuit. When this happens, fuses pop, wires melt, and the "smoke is let out" of the circuit. Every circuit must have some type of load or resistance (lightbulb).

For safety, mention that a good mechanic always prevents electrical sparks near the battery for fear of igniting hydrogen gas released by the battery.  Also, when disconnecting any power (positive) wire, the battery ground cable should be disconnected.

#### Resources and Materials

• Draw a simple series circuit on the board using wiring schematic symbols (see attached notes). The students must take notes from the lesson.  A standard rule is if it is on the board, then it is in your notes.  The circuit must model the light board series circuit with a battery, a fuse, wires, three resistors / bulbs and grounds. Explain how current moves through the curcuit (conventional theory).

Then grab the test light and model hooking it up to the circuit to test power. The test light clip must be hooked up to ground (negative battery post). Have students anticipate and comment what they think will happen has the test light metal tip is moved through the circuit. The test light should be bright before the first bulb and dim as it moves across each bulb until you reach the ground side (test light goes out).

Ask for an explanation on why the test light went out. Ask how the ground side should be tested.

Model hooking the the test light to power (positive battery post). Now move the test light metal tip again through the drawn circuit. Have the students anticipate and comment what the test light should show. The test light should only light on the ground side of the circuit.

#### Resources and Materials

• Light Board Demo Demo / Modeling

Now go back to the light board.  Add a fuse on the power side. Model exactly how to check the power and ground using a test light. Model it with a good fuse and blown fuse. Discuss what to look for when theire is a bad fuse (power on one side and not the other). Also, if your battery pack has an on/off switch, turn the power off and show what to expect when there is no power (fuse is dead on both sides). Try to have the student lead the discussion, and use their prior knowledge.

• Vehicle Modeling Demo / Modeling

Have the students put away their notes and put on their safety glasses. Prep a car with a blown fuse and bad body ground. Go out to the car and hook the test light to the negative terminal of battery. Explain that when you use a test light, you must always check the bulb by connecting it to both battery terminals first. Verify the test light "bulb" is okay and illuminates. Check the fuses in the engine compartment. Identify the good fuses, bad fuse, and fuse that is dead. A "think aloud" is an ideal strategy for students to understand your thinking. Switch the test light to the positive terminal of the battery. Touch the test light all over the car body, frame, motor to show anything metal is ground. Then proceed to test the negative battery cable and all body grounds. Connect it back to the classroom lesson.

• Test Light Review Demo / Modeling

When students are seated, review how to use a test light using the tool chest and light board again. Ask students where to hook up the test light to check power and ground on both examples. Go over what to expect with good, bad, and dead fuses. Hand out the lab activity and explain you will monitor them and stamp their paper when the whole group/team demonstrates the proper use of a test light to check fuses and grounds.

• Have the students put on their safety glasses and assign vehicles that have a bad fuse and ground. Dismiss the students to the lab as teams. Rotate and monitor through the groups asking open ended questions to check for understanding. (Example: What are you testing and how is the test light hooked up for your test). It is a good idea to give one or two groups a test light with a bad bulb (the word gets out quick!). When students achieve proficiency, stamp their papers.