Electricity 101 Part 4: Circuit Diagrams


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Electricity 101 Part 4: Circuit Diagrams

Postby WingAdmin » Sun Jan 19, 2014 12:07 pm



Part 3: Circuit diagrams

The circuit (or schematic) diagram is something that seems to scare most people who are unfamiliar with electronics. They look at something like this schematic from a 1982 GL1100 Aspencade, and it looks like a indecipherable mess:

1982 GL1100A Schematic Diagram
1982 GL1100A Schematic Diagram


And in fact, this diagram is a bit of an indecipherable mess. It is at the upper limit for what I would consider to be a readable, usable schematic diagram. When I had my GL1100, I enlarged this diagram and printed it out poster-size, so that I could have a chance of following the lines accurately.

What this diagram shows is every wire, component and connector in the bike, and how each thing connects to every other thing. Every black line on the diagram represents a wire. Unless specified on the diagram, the lines don't specify the specific location and layout of wires - for instance, if the diagram shows two wires next to one another, that doesn't necessarily mean that they will be located anywhere near one another on the bike. The diagram is laid out for readability.

Schematic diagrams use very specific symbols to represent components. Here are a few:

Circuit Components
Circuit Components


Of course, Honda has to do things its own way, and so uses quite a few unique, nonstandard symbols to denote various components. Let's have a look at some of the component symbols they use in the GL1100 diagram. Some of them are obvious:

Obvious Honda Component Symbols
Obvious Honda Component Symbols


Some of them are not so obvious:

Ignition Switch
Ignition Switch


And in some cases, they just give up and use a box to represent an item or module:

Box components
Box components


In this article, I will cover not so much the industry-standard symbols and nomenclature, as what you will find in Honda service manuals. We'll go through diagnosing a simple electrical problem utilizing the schematic diagram to guide us.

As you may have noticed in your bike, the wires are multicolored. Some of them are solid colors:



Some of them have a stripe - they will contain mostly one color, with a thin stripe of a different color:



In the case of striped wires, the main color is always specified first. So a green wire with a yellow stripe would be referred to as Green/Yellow.

Every wire on the diagram will be marked with a letter code to specify its color. At the bottom of every diagram, you'll see a wire color index so you know what those codes represent:

Wire color code
Wire color code


With the advent of the GL1500, the complexity and sheer size of the circuits in the bike meant that there was no possible way to show the entire thing in one diagram. So instead, the circuits are broken down into systems, with each diagram showing only the circuitry and components related to that one system. For instance, let's have a look at the GL1500 cooling system circuit diagram:

GL1500 Cooling Circuit Diagram
GL1500 Cooling Circuit Diagram


This is much easier to read and figure out what is going on. Note that quite a few wires cross over one another - this is necessary, simply because there's no way to fit the diagram on the page otherwise. However, this does NOT mean that they are connected to one another. The only time wires that cross over one another are actually connected together is when there is a DOT over the intersection of the wires, as can be see in the diagram below on the BLK wires.

Let's say we have a problem - the cooling fans aren't turning on when they are supposed to. First, we figure out how the fans are switched on. Looking at this part of the diagram, we can find the thermostatic switch:

Cooling Fans Diagnostics 1
Cooling Fans Diagnostics 1


We can see that the power to run the fans comes in on the blue wires (marked BLU). We can see that each fan is connected with a two-position connector, and that connector is black in color (2P-BLK). We can see that the power, after going through the fans, runs through black wires (marked BLK) to the thermostatic switch. This thermostatic switch is connected to ground (via the engine case, which is grounded, just like the frame, and pretty much every other piece of metal on the bike).

From this we can deduce that the thermostatic switch is open when the engine is cool. When the engine gets too hot, the switch closes, connecting the black wire to ground, completing the circuit, and allowing the power to flow through the fans. As a result, the fans turn on, which in turn cools the engine. When the engine cools off, the thermostatic switch opens, and the fans turn off.

There are two things we can test at this point:

1. Is the switch connecting the black wire to ground when the engine is hot?
2. Are the fans receiving power on the blue wires?

If only ONE of the fans was not working, we also have some good information: We can see that the wires connecting the fans to the switch and to power for each fan are connected together - so if one fan is running, the other fan should be as well. If that is the case, we could check the 2P-BLK connector of the inoperable fan and see if it has power on the blue wire, and ground on the black wire (when the engine is hot). If it does, then the fan itself is the problem.

But back to our two-fan problem. Let's check our first item, whether the switch is connecting to ground. We don't have to get the engine hot for this: All we have to do is bypass the switch. At the thermostatic switch, we would disconnect the black wire from the switch, and push it against the engine case, which connects it to ground. If the fans turn on, then we know that the switch is not working correctly, and needs to be replaced.

Let's assume the fans did not turn on, meaning that the switch is probably not the problem. Next, we check to see if there is 12 volts on the blue wire, on the 2P-BLK connector (this is the connector the fans plug into).

We do this using a multimeter, as explained in part two of this series. One lead of the multimeter goes into the blue wire, the other goes against a known good ground. Here's what we see:

Image

That tells us that there is no voltage at the fans. This tells us that the problem is likely not with the fans or the thermostatic switch. We have to move further up the diagram.

Cooling Fans Diagnostics 2
Cooling Fans Diagnostics 2


Moving up the blue wire, we see it comes to a six-conductor "mini" connector, and that it is red in color (6P-RED mini). At that point, notice that the blue wire changes over to a BLK/BLU wire - a black wire with a blue stripe. So we now trace the black/blue wire up and find it is connected to fuse 4, in the fuse box. That's our next diagnostic step.

Open up the fuse box, pull fuse 4, and see if it is blown. In this case, the fuse is blown. We replace it with a new 10 amp fuse, and our fans come back to life.


But how do we find all of these connectors in order to test them? On the earlier four-cylinder Wings, you are left to tracing wires along the wiring harness, or asking the friendly people in a forum. Starting with the GL1200 Limited, Honda produced a separate Electrical Troubleshooting Manual. For the GL1800, this manual was folded into the main Service Manual. This wonderful, helpful book tells us exactly where to find every electrical device in the bike.

To start with, the ETM separates every circuit even more, into very simple block diagrams:

ETM Fan circuit
ETM Fan circuit


This diagram shows us that the 2P-BLK connector on the left fan is connector C109, the equivalent connector on the right fan is C110, and the 6P-RED (mini) connector is C22. Elsewhere in the CTM, we have a listing of each connector, and a description of its location:

ETM Connector Locations
ETM Connector Locations


Not only that, each one refers to a picture that shows exactly where each connector is located:

ETM Location Image 21
ETM Location Image 21

ETM Location Image 52 and 53
ETM Location Image 52 and 53


This helps greatly in tracing down electrical issues, and I urge you strongly to purchase the Honda service and ETM manuals if you intend on doing any of your own service work.


Back to our fans. Where does fuse 4 get its power from? Let's trace backward a bit more and have a look. The power for fuse 4 comes from a Blue/Orange wire that we can follow back to the ignition switch:

Cooling Fans Diagnostics 3
Cooling Fans Diagnostics 3


And from there, it connects through the switch when it is in the "ON" setting, directly to the red wire, which runs through the solenoid and master fuse and connects directly to the battery:

Cooling Fans Diagnostics 4
Cooling Fans Diagnostics 4


The ignition switch looks a bit complicated, but it's really not. It's just a bunch of connectors that are connected to one another in various combinations depending on the position of the switch.

GL1500 Ignition switch
GL1500 Ignition switch


The position of the switch is in the list down the left side, and the terminals (or wires) are across the top). It shows us that in LOCK and OFF, none of the connectors are connected to one another.

In the ACC position, the red (which is +12V coming from the battery) is connected to the ACC terminal, which means anything connected to that ACC terminal will have power.

In the ON position, the red is connected to black (which is the main wire that runs the entire bike), ACC (to run accessories), as well as the Blu/Orn wire, which we already know powers fuse 4, and the fans. It also connects TL1 and TL2 together, which are used to illuminate the tail lights.

Lastly, we have the P (park) position, where the red incoming battery power is connected to ACC as wel as the specal "P" circuit which illuminates the taillights.

The last thing we'll talk about are relays:

Relay
Relay


A relay is a special kind of switch. It doesn't have a button to actuate it, instead it has a coil of wire. When power is sent through this coil, it creates an electromagnetic attraction to the switch, and closes (or opens, depending on the relay) the switch. This is used for one circuit to control a different circuit, without actually having to connect the two circuits together.

In the diagram above, there is switched power coming into the relay on the white wire, and out the green (because in Honda world green is ground). When the power is applied to the white wire in the relay, it closes the relay, which allows power to flow from Fuse 8, across the relay, and out on the Brown/Blue wire.

Why would we need to do this? A very good example is the starter relay. The wires running to your starter are huge, in order to be able to carry enough current to crank the engine over. Running these huge wires up to your starter button would be crazy, and the starter button itself would have to be huge, in order to handle the current.

Instead, a small starter button is used, and it controls a very small amount of current. This current is used to actuate the starter relay, which then closes and engages the starter.

The GL1500 and GL1800 make very extensive use of relays, and there are a LOT of them. Relays are mechanical devices, and over time they will fail.

Tracing circuits through schematic diagrams is an excellent way to figure out the electrical systems of your bike. I would suggest photocopying circuit diagrams so that you can trace circuits using a highlighter pen. As always, if you have any questions, please feel free to ask!



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redial
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Re: Electricity 101 Part 4: Circuit Diagrams

Postby redial » Sun Jan 19, 2014 5:30 pm

Excellent! That took more than a couple of minutes to compile, and thank you for your comprehensive, but simple explanations, so that even foreignors can understand them. Great work, thanks.
Len in Kapunda

The world is not going to finish today, as it is already tomorrow in Australia and New Zealand, and other islands of foreign nations such as Guam and Samoa.

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Re: Electricity 101 Part 4: Circuit Diagrams

Postby bustedwing » Sun Jan 26, 2014 5:32 pm

Electrical troubleshooting has always been one of my strengths when everyone else shys away. My son in law who is an owner/operator of a logging truck business hates electrical troubleshooting but concedes with more electronic devices in use today it's something you'd better get used to.
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Re: Electricity 101 Part 4: Circuit Diagrams

Postby bustedwing » Sun Jan 26, 2014 5:45 pm

I wanted to add thank you Wing for taking the time to do this. It was well written and easy to understand, and to someone that is just starting out doing their own repairs it would be a huge advantage. And probably convince someone that electric repairs are not that tough.
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Re: Electricity 101 Part 4: Circuit Diagrams

Postby seelyark1 » Tue Feb 11, 2014 9:54 am

Outstanding article! I have done some electrical trouble shooting on my own wing. Seems that I have a, or had a rat that wanted to build a nest under the fairing, and liked to chew on the wires. I did it the old fashioned way of looking to see which wires were the problem as I couldnt read the schematic. These old eyes aren't what they used to be. After reading this article, I am going to see about this manual. Am I correct that they make it for the 1500 too? Having eye surgery this week, so no riding for a day or two. But if it works as well as the other one was, will be 20-20 without glasses. Then maybe I could see the schematic.
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Re: Electricity 101 Part 4: Circuit Diagrams

Postby WingAdmin » Tue Feb 11, 2014 12:31 pm

seelyark1 wrote:Outstanding article! I have done some electrical trouble shooting on my own wing. Seems that I have a, or had a rat that wanted to build a nest under the fairing, and liked to chew on the wires. I did it the old fashioned way of looking to see which wires were the problem as I couldnt read the schematic. These old eyes aren't what they used to be. After reading this article, I am going to see about this manual. Am I correct that they make it for the 1500 too? Having eye surgery this week, so no riding for a day or two. But if it works as well as the other one was, will be 20-20 without glasses. Then maybe I could see the schematic.


Most of the diagrams in this article are FROM the GL1500 service and Electrical Troubleshooting Manuals. But I'm with you, I definitely need to use glasses to follow those fine wires on the diagrams. A lot of the time I will put it on the computer screen and then magnify it on the screen in order to follow the wires.

ianstaley
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Re: Electricity 101 Part 4: Circuit Diagrams

Postby ianstaley » Sat Mar 15, 2014 5:49 pm

This has to be the biggest Voodoo of any car or biker contemplating a rebuild or fault finding. This has cleared the fog a little for me so thanks.




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