Electrical Circuit Inspection Procedure

Check Open Circuit

1. Procedures for Open Circuit
   1. Continuity Check
   2. Voltage Check

   If an open circuit occurs (as seen in [Fig 1]), it can be found by performing Step 2 (Continuity Check Method) or Step  3 (Voltage Check Method) as shown below.

   Fig 1: Checking Open Circuit

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2. Continuity Check Method
   NOTE: When measuring for resistance, lightly shake the wire harness above and below or from side to side.

   Specification (Resistance) 

   1Ω or less Normal Circuit

   1MΩ or Higher Open Circuit

   1. Disconnect connectors (A), (C) and measure resistance between connector (A) and (C) as shown in [Fig 2].

      In [Fig 2.] the measured resistance of line 1 and 2 is higher than 1M and below 1 respectively. Specifically the open circuit is line 1 (Line 2 is normal). To find exact break point, check sub line of line 1 as described in next step.

      Fig 2: Measuring Resistance Between Connector (A) And (C)

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   2. Disconnect connector (B), and measure for resistance between connector (C) and (B1) and between (B2) and (A) as shown in [Fig 3].

      In this case the measured resistance between connector (C) and (B1) is higher than 1M and the open circuit is between terminal 1 of connector (C) and terminal 1 of connector (B1).

      Fig 3: Measuring Resistance Between Connector (C) And (B1) And Between (B2) And (A)

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3. Voltage Check Method
   1. With each connector still connected, measure the voltage between the chassis ground and terminal 1 of each connectors (A), (B) and (C) as shown in [Fig 4].

   The measured voltage of each connector is 5V, 5V and 0V respectively. So the open circuit is between connector (C) and (B).

   Fig 4: Measuring Voltage Between Chassis Ground And Terminal 1 Of Each Connectors (A), (B) And (C)

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   ■ Check Short Circuit 

   1. Test Method for Short to Ground Circuit
      1. Continuity Check with Chassis Ground

      If short to ground circuit occurs as shown in [Fig 5], the broken point can be found by performing Step 2 (Continuity Check Method with Chassis Ground) as shown below.

      Fig 5: Checking Short Circuit

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   2. Continuity Check Method (with Chassis Ground)
      NOTE: Lightly shake the wire harness above and below, or from side to side when measuring the resistance.

      Specification (Resistance) 

      1Ω or less Short to Ground Circuit

      1MΩ or Higher Normal Circuit

      1. Disconnect connectors (A), (C) and measure for resistance between connector (A) and Chassis Ground as shown in [Fig 6].

         The measured resistance of line 1 and 2 in this example is below 1 and higher than 1M respectively.

         Specifically the short to ground circuit is line 1 (Line 2 is normal). To find exact broken point, check the sub line of line 1 as described in the following step.

         Fig 6: Measuring Resistance Between Connector (A) And Chassis Ground

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      2. Disconnect connector (B), and measure the resistance between connector (A) and chassis ground, and between (B1) and chassis ground as shown in [Fig 7].

      The measured resistance between connector (B1) and chassis ground is 1 or less. The short to ground circuit is between terminal 1 of connector (C) and terminal 1 of connector (B1).

      Fig 7: Measuring Resistance Between Connector (A) And (B1) And Chassis Ground

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■ Testing For Voltage Drop 

This test checks for voltage drop along a wire, or through a connection or switch.

1. Connect the positive lead of a voltmeter to the end of the wire (or to the side of the connector or switch) closest to the battery.
2. Connect the negative lead to the other end of the wire. (or the other side of the connector or switch)
3. Operate the circuit.
4. The voltmeter will show the difference in voltage between the two points. A difference, or drop of more than 0.1 volts (50mV in 5V circuits), may indicate a problem. Check the circuit for loose or dirty connections.
   Fig 8: Checking Voltage Drop Across Wire

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