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States of a Wire

Modern electrical systems can be complex. Under-

standing different failures that can happen to the wires

that connect components can reduce troubleshoot-

ing time and ensure correct repairs. Using the proper

wiring diagram will help you isolate the specic wiresused in the circuit so you can quickly perform the

required tests to locate the failure.

Normal

A perfectly good wire. The wire will not affect the

normal operation of a circuit. In motorsports applica-

tions, a wire should show very little voltage drop when

current is owing through it. A maximum of 0.2 VDC is

an acceptable reading.

2013 Yamaha Motor Corporation, U.S.A. All rights reserved

December 2013

Short

A shorted wire has path to ground before the circuits

load. This is also referred to as a dead short. In this

case the load in the circuit has been bypassed. The

power source will now push as much current through

the circuit as possible, several hundred amps in thecase of most motorsports batteries. This will blow the

fuse for that circuit.

To locate the short in the circuit, replace the fuse with

a small light bulb (an old motorcycle turn signal works

well). While the short is present, the bulb will remain

lit. When the short is located and repaired, the bulb

will go out. Replace the fuse and verify proper circuit

operation.

If the short has some resistance to ground it may not

blow the fuse, but can cause excessive amperage toow through the circuit. This can cause connectors

or the insulation on the wire to get to hot and start to

melt. Remove the fuse and again use the bulb in its

place. This will once again allow you to nd the short.

Open

An open wire is physically broken and will not allow

current to ow through it. The circuit will not function.

Since no current is owing through the circuit, no volt-

age drop will be seen across the circuits load. Supply

voltage will be available from the voltage source to the

open. No voltage will be available after the open.

Use a volt meter to follow the positive side of the cir-

cuit. The voltage will stop where the open is.

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Grounded

Some circuits are controlled on the ground side of the

load. These circuits may use relays as the switch to

control current ow through the circuit. This will allow

the ECU to control the circuit. An electric fuel pumps

circuit is a good example. A grounded circuit will have

a path to ground after the load but before the control-

ling switch, in this case the ECU. This will cause the

circuit to be always active, the ECU will not be able toturn the circuit off.

Now that the failure has been determined to be

between the relay and the ECU, a few more quicktests will isolate the failure down to the affected wire

or connector.

Performing a voltage drop test on portions of the

circuit will quickly locate the unwanted resistance. To

quickly isolate which side of the circuit the failure is

in, perform a voltage drop on the entire positive side.If the reading is acceptable, repeat the test on the

ground side of the load.

For more information on performing a voltage

drop test refer to the March 2013 Issue of the

Service Limit, Voltage Drop Testing.

Understanding how different wire failures affect a

circuit allows you to quickly decide what is the most

effective testing procedure. This will cut down on

diagnostic time and helps ensure that the failure is

correctly identied and repaired.

Start by locating the ground and disconnect it, 1.

Disconnect the next connection as you move towardsthe load, point2. Disconnecting the circuit at everyconnection. When the load in the circuit stops operat-

ing you have just isolated the failed wire, point 3.

Series Resistance

In a normal circuit, the load should be the only resis-

tance in the circuit. Series resistance is an unwanted

additional load in the circuit. This unwanted resistance

will consume some of the available voltage. When

this occurs, circuits may not operate correctly and can

often begin to operate in very unpredictable ways.

This is particularly true when the resistance affects

the sensors used on modern fuel injected units.

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