Diagnosing an OPEN CIRCUIT

Diagnosing an OPEN CIRCUIT

By Brian OLeary

Open Ended

What is an open circuit?

An open circuit is defined as an electrical circuit in which current does NOT flow.

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​Remember the flow?

​Open Circuit

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In simple terms, the circuit is not complete.

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There is no continuity​....

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​Continuity is two or more things electronically connected

Open Circuit

​Electrical Continuity

• A complete circuit has continuity (lighting system, horn system)

• A coil of wire has continuity (Relay coil, injector coil, Solenoid coil)

• A closed switch has continuity (headlight switch, ignition switch)

• A good bulb has continuity (Light)

• A good resistor has continuity (Heat)

• A good motor has continuity (Motion)

Electrical Unit 4

Name something in this room with ​continuity

Multiple Choice

A forward biased diode has continuity through both sides.

• True

• False

Multiple Choice

A complete circuit is defined as _.

• an electrical circuit that flows voltage

• an electrical circuit that does not flow voltage

• an electrical circuit that does not allow the flow of current

• an electrical circuit that does flow current

Draw

Draw a complete circuit. Include a Source, Load, Conductor.

Continuity Test

What tool is used to test continuity?

Ω​ Ω Ω​

OHMS!

Testing for resistance!

​Testing a wire, resistor, motor, any kind of electrical device for resistance.

Every load will have resistance, If OL, that load has an open circuit internally

​Continuity Test Settings

Some DMM's have a continuity test setting that will beep when the circuit or load has continuity. Test leads are placed at opposite ends of the load or circuit.

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​Some text here about the topic of discussion.

​Continuity Test Settings

Multiple Select

Which multimeter position is used to test continuity?

If the circuit is too long, test the circuit from connector to connector using the in-line connectors of that circuit. ​

​Connector to Connector

Using the DMM, Install the test leads at both ends of the circuit to test continuity between the leads.

​End to End

How to test circuit continuity of a wire

Problem solving and critical thinking involved. ​

Poll

If you are attempting to test continuity from the brake light switch to the brake lights and your test leads are not long enough, what is your solution?

• Get longer test leads?

• Make longer test leads?

• Check continuity from in-line connector to in-line connector?

• Give up and let someone else do it?

GAME!!!

Test the continuity of the wire in front of you. If continuity is present, connect your wire to the tables wire next to yours to create one long circuit.

Now test the continuity of the entire circuit from end to end.

Although a circuit may have have continuity or low resistance from end to end, can that circuit carry sufficient current?

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The wire must be large enough to carry the current needed.

Load Testing a Wire

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Open Ended

A rodent chews through a wire that goes to a headlight bulb connector. The headlight bulb will use 30 amps of current. You, as the technician, are to repair the circuit. You grab a length of wire you have laying around. The wire you have is a 20 gauge wire. If this sufficient? What will happen if you install this wire instead of the 14 gauge wire that it calls for?

Install a strand of wire

One table will install a single strand of wire into the length of wire that we created.

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Check the continuity of the length of wire again. Do we have continuity?

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Lets load test this circuit....​

Subject | Subject

this should be interesting

Open Ended

How would you test the integrity or continuity of a circuit from the front of the car to the back of the car if your meter leads do not reach?

If your meter leads are not long enough to test a continuity of a circuit from end to end, you must test from connector to connector...

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​Testing a long circuit.

Open Ended

What do you think an in-line connector is?

In-line connectors are connectors that are in series of the circuit. In-line connectors may be used when running wires between panels or along different parts of the vehicle​.

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In-line connectors allow us to disconnect a whole harness without disconnecting each individual component

In-line Connectors

Circuit testing at connectors...

ALWAYS use the correct test terminals

Loose connections are one of the leading leaders of circuit problems. A loose connection creates high resistance in a circuit. High resistance drops voltage. Voltage drop before or after the load causes poor performance of the load or sensor. ​

Multiple Choice

AllData does not give any information on connectors...

• False

• True

Open Ended

If you are diagnosing a long circuit such as a brake light circuit or a trailer connector circuit, what information from your service manual do you think you may need?

Match

Match the description to the name

• Schematic

• Connector View

• Harness Routing Diagram

• Temperature Vs Resistance Chart

• Description and Operation

Diagram of wiring for a system

A picture of the connector and its terminals

A picture showing how a harness is run through the vehicle

A table showing the ohm value to temperature reading

How a certain system or component works

• Diagram of wiring for a system

• A picture of the connector and its terminals

• A picture showing how a harness is run through the vehicle

• A table showing the ohm value to temperature reading

• How a certain system or component works

Open Ended

Why is load testing a circuit better than testing the continuity of a circuit?

Open Ended

Reflection:

What did you learn from today?