Power and Ground

Power and Ground

By Brian OLeary

Power is the voltage (electrical pressure) or the current (electricity flow) present. ​

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What is POWER?

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Electrical POWER is needed for electrical devices to function. A bulb, a motor, or a heater cannot function correctly if it does not receive any power or the correct amount of power.

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POWER!!!!!

The POWER Side...

​Where is the power?

The POWER is the hot side, the battery voltage side, the B+ side. Power wires can be any color, but most likely a red, yellow, pink, or orange wire is the power wire. You will have to use a wiring diagram or schematic to figure out where the power comes from. ​

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Multiple Choice

What is POWER?

• Resistance

• Current

• Ground

• Frame

A digital multimeter is used to test for POWER. The red test lead is used at the power wire, the black test lead is used on the negative battery post or a good ground​

​​Testing for POWER

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​A test light can be used to find POWER. A test light clamp is clamped to the negative post or a good ground and the test light probe touches a power source. A light will emit

​​MO POWA!!!

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​A test light is a simple circuit without the source. A test light has a screw driver handle with a light bulb inside. The light bulb is connected to the metal tip of the test light on one end and the test light cord with clamp on the other end.

Test Lights

​With the test light, connect the clamp end to a known good ground and probe the pointed end to a power source (fuse, positive cable, wire with voltage). The light inside should illuminate indicating the presence of power AND a good ground.

Test Light

Multiple Select

When testing circuits for power using a test light, if the test light does not illuminate, that means...

• Little resistance is present

• Voltage is not present

• The test light could be connected to a bad ground.

• Current is flowing to the test light

An LED test light is high impedance. Low amount of current is needed to light an LED therefore a high impedance test light tests for low current. Safe for Computers or modules.

High Impedance

A light bulb test light is low impedance. A higher current draw will occur using a light bulb because it requires more current to light up. Great for testing high current or heavy load circuits.

Low Impedance

Types of Test Lights

A test light can be used in place of a load. If testing a load such as a pump, light, horn, heater, solenoid, or motor, connect the test light between the power and ground circuits and command the load on. If the test light illuminates, power and ground are assumed good to the load. If testing a load with a current draw above 5A, use a low impedance test light.

Test Lights

Multiple Choice

Which test light is safe for computer or module circuits?

• High Impedance

• Low Impedance

Poll

What would be your go to tool to test for power?

• Test Light

• Ammeter

• Digital Multimeter

• Scan Tool

Power can be found at the battery, fuse, any load, in a wire, at a sensor, ​to a connector, or the alternator.

Where is the power?

Multiple Choice

Power can be found at any of these except

• Light Bulb

• Negative Terminal

• Fuse Panel

• Positive Terminal

Ground....

​We're going to hit the ground running

Open Ended

What do you think the ground is?

The Ground

​My negative side...

The ground is the negative side of the battery. This is the return. Remember the LOOP? The power side is the side with the current, the ground side is the path that finishes that LOOP (A complete circuit). ​

​If you don't get this, you're GROUNDED!!

The ground is the path that returns to the negative side of the battery. The ground can be the engine, the vehicle body, the frame, or any metal component attached to the frame or body​

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​Hit The Ground!

Multiple Choice

This is a good ground?

• Vehicle frame

• Vehicle Body

• The metal engine

• All of the above

The ground has no power, so to test the ground, you have to test the resistance of the path​

How do you test the ground?​

Testing Ground

​Resistance

To test the ground, you use the multimeter to test for resistance. Turn the dial on the DMM to the Ohm symbol. Measure end to end of the ground path. Low resistance is good. High resistance means there is a loose connection, corrosion, rust, or some kind of substance causing restistance.

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Draw

What is the symbol for a ground?

Poll

What tool is used to test the ground?

• Multimeter

• Test light

• Ammeter

• Ground Meter