Honda VT750CD ACE, Electrical Repair And Modification

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Honda VT750CD ACE
18 Electrical Repair and Modification
4.0 Troubleshooting & Emergency Roadside Repairs
4.1 Introduction
Eventually, every motorcycle owner has a problem with their bike's electrical system. If you are lucky, it's a
simple problem that happens in your driveway that you can get your dealer to fix. However, we should all be
prepared for problems happening on the road, when we are far from any garages and their help. I'll try to offer
some basic troubleshooting tips here as well as techniques for repairing those problems on the side of the road,
so you can get the bike back home.
4.2 Troubleshooting
There are some basic things you must know before you can troubleshoot an electrical problem. First, all circuits
on a motorcycle have four basic requirements... Power Supply, Conductor, Load and a Switch.
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Power Supply is the battery. It is NOT the alternator! All power for all systems on a motorcycle comes
directly from the battery. The alternator is only used to charge the battery and prevent it from
becoming depleted during normal use.
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Conductors are the wires
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Loads are the devices that actually consume electricity to operate. Examples would be a light bulb,
starter motor, horn, etc. All circuits have a load. Even if you just jumper two wires across a battery,
then the wires would then become the load as well as a conductor and they would consume electricity
to produce heat.
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Switches are the devices used to control the circuit. They can be mechanical (ex: turn signal switch) or
electronic (ex: transistor)
Next, there are three unwanted circuit conditions that we will run into on our motorcycles. They are Open,
Shorted and Grounded. It is important to learn how to recognize what type of failure you have in your electrical
system.
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An Open circuit is one where the power does not reach the load. Usually caused by an open fuse,
broken wire or a faulty switch
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A Short Circuit is one where the power is 'shorted' to ground before the load. This usually results in a
blown fuse or circuit breaker. It can be a wire that is cut or chaffed through and shorting to the frame
or, again, by a faulty switch. Sometimes it can also be a sealed electronic unit that has failed internally,
causing a shorted condition. Examples of this would be a sealed turn signal relay, starter solenoid or
ICM box
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A Grounded Circuit is one where the power is shorted to ground after the load but before the switch or
controlling device. So the load may be powered (light on for example) but there is no control over it.
There are two basic tools that can help you troubleshoot almost every electrical problem… the multimeter and
the test light. A test light is nothing more then a 12 volt light with two leads that allows you to quickly and
easily check for power in a circuit. The multimeter can also do this, but it has many, many other functions. It
can check continuity, test diodes, measure resistance and check for bad grounds, measure amperage draw…
the list is endless. And these days, you can buy a really decent multimeter for very little money.
Make sure to read the instructions that came with the multimeter before attempting to use it on your
motorcycle. Here are some basic guidelines for the use of multimeters in troubleshooting...