How to read wiring diagrams

Jef · Dec 10, 2014

I'm hashing out a video on this topic, so this is sort of a dry run kind of thing....

So, what does all this mean?

Lets break it down into smaller pieces

The numbers along the bottom are the "Current Tracks"

The more information in a given wiring diagram, the higher up the Current Tracks will count to.

The Current Tracks represent vertical columns

Rule of thumb, positive power is at the top and is ground is at the bottom. The large grey box across the top is the Power Source. This can be a relay panel for example. The thin line at the bottom is ground, more on this later.

Now we start adding "wires", vertical lines. The boxes with numbers in them at the ends of the lines represent a Current Track number. In Current Track number 97, there is a line with a box that has "102" in the box. On Current Track 102, there is a line with a box that has "97" in it. The wire in Current Track 97 continues over at Current Track 102, physically the same wire in the car.

The circle with numbers in them represent two different things, one is a weld point, the other a chassis ground location. The circle with 367 is a weld point, the thin horizontal line from Current Track 104 to 106 shows that those points are electrically tied together. A weld point is 3 or more wires mechanically and electrically joined together.

The circles with 609 and 675 in them are ground points. In most cases, a lug secured to a threaded stud on the body of the vehicle.

Note that on Current Track 108, the wire turn to the right and runs to the end of the image and has an "a" next to it. This means the wire information continues on the next page, it will have an "a" on it as well. If more than one wire is drawn this way in a diagram, then the next wire will have "b", then "c" and so on.

Upper left, ground point. Upper right, weld point (sonic weld) example. Bottom, terminals on threaded studs, more on this later.

.... continued on the next post.....

Jef · Dec 10, 2014

Information about the physical wires is now added, wire size and color. Look at Current Track 97, the .5 is for a 0.5mm diameter sized wire, and the bl/ro means it is a blue wire with a thin red trace line on it. Remember how the boxes with the numbers at the ends of the vertical lines represents the wire continuing on another Current Track. Current Track 97 has a wire that continues over on Current Track 102, again a 0.5mm diameter wire, blue with a red trace, same wire.

And take a look at weld point 367, Current Tracks 104 and 106, while different wire sizes, they both have the same color wire, brown with black trace. Wait... how are you getting brown wire with a black trace line on it from "br/sw". Sure, I can see "br" as brown, but "sw" as black... are you crazy. Yes... and more on this later (wire color info as well).

Current Track 96, few things to point out, at the top we have a 2.0mm diameter wire, red with yellow trace is now electrically connected to a power source, a Terminal 15 source (ignition turned on). Power at top. Then there is a 2.0mm diameter wire, solid brown, that is grounded at location 609. Power feeds tend to be red, grounds tend to be brown, but there are exceptions to this rule in every car.

Hardware is now added, the grey boxes. These could be about anything that isn't wiring. A control module, sensor, solenoid valve, etc. The larger one has an arrow at the end of it pointing to the right, this means it continues on the next page. Note that is has a "PNP transistor" schematic symbol on it. Rule of thumb, that means it is a smart device, it performs some sort of action (output) based on data (input).

The smaller box also has schematic symbols in it, a variable resistor and electric motor. The factory wiring diagrams more use standard schematic symbols, you can Google search examples of this.

If you look carefully at this image, you will also see little "W" and "M" looking items where the wires meet the hardware. Hardware, such as a control module or relay, has male electrical contacts, tabs. The wiring harness will have the female receptacle crimped onto the ends of the wires, timers. The generic term for these tabs and timers is a "terminal" which can get confusing because the term "terminal" can also refer to types of electrical connections... confusing stuff folks.

Now we are starting to identify the physical locations of terminals and also adding Component Locators to the hardware.

Where each wire connects to a piece of hardware now, we have a Txx/yy values. The T is the physical plastic terminal housing, xx is the total number of positions the in the plastic housing, yy is what number position that wire and terminal are fitted to. On Current Track 108, we see T16/2. The T16 means the plastic terminal housing that is connected up to that piece of hardware has 16 positions in which wires can be fitted. The /2 means that 2.0mm red wire with green trace is fitted into position #2 on that terminal housing. Just because this T16 has 16 positions in it, it doesn't guarantee it will have 16 wires coming out of it.

On Current Tracks 104 and 106, we see T4c/x values listed. So the T4 means the plastic terminal housing has 4 positions. But there are going to be a other terminal housings in the vehicle with 4 positions, so they start putting a lower case letter in there. This T4c means that somewhere else in the car are at least three other 4 positions plastic terminal housings in there... T4, then T4a and T4b. For all we know, there could be seven more after this, so a T4j could be somewhere in the car.

The Component Locators are in most cases letter/number combo. In the example we have J404, G99 and V211. There is a logic in how this work, "J"s are some sort of control module, engine, ABS, airbag and so on. "G"s are sensors of some sort. "V"s are electric motors. There are others as well, "N" are solenoids, "M"s are lights, "F"s are switches.

Here is a picture of a terminal housing, it has 14 positions, so a T14. Note that there are only 10 wires coming out of it. And and in a few cases, you will find where two wires are crimped together, so you might have more wires than positions.

It is a bit difficult to see, but there are numbers molded into the terminal housing, The top row has even numbers, 14 on the left, 2 on the right. Odd numbers are on the bottom. The top row, left most wire is in position 10, thus T14/10 is a black wire with green trace.

So that is a lot of crap to remember.... how am I to keep up with all this stuff? Luckily, every wiring diagram has a cheat sheet right there on it....

Each page will have relevant information on it. At the top is the listing of what systems we are looking at, Muffler bearing Controller in this example. Then we have a list with descriptions of the items shown. Weld points and ground locations are briefly described as well, some will be more detailed than others. And at the bottom, the codes for wiring colors. These are German abbreviations. The German word for "black" is "schwarz", hence how we get black is "sw". Same concept for the other colors as well. This is refereed to as Gernglish.

So I hope this gives you a basic understanding of how the wiring diagram is laid out a better understanding of the information.

Again, this is a dry run for a future video on this topic. Suggestions welcome.

Jack@European_Parts · Dec 10, 2014

Now we start adding "wires", vertical lines. The boxes with numbers in them at the ends of the lines represent a Current Track number. In Current Track number 97, there is a line with a box that has "102" in the box. On Current Track 102, there is a line with a box that has "97" in it. The wire in Current Track 97 continues over at Current Track 97, physically the same wire in the car.

I like to reference that BOX as a STAR-GATE because some WD support a hyperlink worm hole to the next track...........

Is the muffler bearing a serious performance enhancer.........?

There are also sections in the factory repair manual labeled how to read wire diagrams........

Zenerdiode · Dec 11, 2014

Hello Jef,

Just a few typos spotted I'm afraid.

You may delete my post when done.

In post #1:

"The wire in Current Track 97 continues over at Current Track 97," should be "The wire in Current Track 97 continues over at Current Track 102,"

In post #2:

"Current Track 97 has a wire that continues over on Current Track 97," should be "Current Track 97 has a wire that continues over on Current Track 102,"

"Where each wire connects to a piece of hardware now, we have a Tyy/yy values." should be "Where each wire connects to a piece of hardware now, we have a Txx/yy values."

I'm not knocking it, it will be great in a video.

Rembrant · Dec 11, 2014

Jack@European_Parts said:
Is the muffler bearing a serious performance enhancer.........?

I don't know about performance, but it does enhance the experience.

Jack@European_Parts said:
There are also sections in the factory repair manual labeled how to read wire diagrams........

I've read these sections, and they helped. I had more trouble actually finding the wiring diagrams for my car than actually reading them.
Once I found them, I was golden.

Another thing I found helpful was to copy/print the one page with all of the electrical symbols on it, so that you can refer to it while reading the wiring diagrams.

Great thread,
Rem

Jef · Dec 11, 2014

Hashing out the hands on example, feel free to play along at home. New concepts shown in this batch of diagrams

Some new concepts shown above:

So we have a grey box, meaning some sort of hardware, fuse block in this example. Notice how the ends of the fuse block are shown with wavy/curved lines. This means there is more to the hardware (fuse block) that being shown. 5 fuses out of maybe 50 position for example.

That thin horizontal line represents some sort of bus strip. Rule of thumb, some sort of metal strip, not stranded copper wiring.

Some details are given about the fuses as well, S242, S15, S239, etc. The "S" is a fuse. Now you need to be careful because cars will often times have more than 1 location for fuses, and depending on which vehicle you are working with, it will be identified via different methods, some using numbers to identify which fuse block, other times letters. In the above example, only numbers are used to identify which fuse block. Other wiring diagrams may have SA4 or SD32, so Fuse Block A, position #4 and Fuse Block D, position 32.

Audi will mix it up even more with something like ST1, ST2 and ST3, which are 3 separate fuse blocks side by side, maybe 12 positions in each, but use the same SB5 term for a fuse... SB5 in ST2 is different than SB5 in ST3. Oh yeah, the Germans are at war with us.

Easy one here, shown is your run of the mill Alternator. The thin line running to the chassis ground point on Current Track 4 means that item is grounded because it is bolted down. There isn't an actual wire.

When wires are drawn as dotted lines, it tends to mean that "maybe this applies to the car you are working on". Normally there will be info on that page of the wiring diagram stating what the dotted line is for. In my example, the dotted line runs to a F36 Clutch Pedal Switch, but if your car is an automatic, there would be no F36. Other times it could be running production changes, you may find note about cars up until 06/2006 use [ABC] and then from 07/2006 the cars use [XYZ], so the wiring diagram will show both variables and often have dotted lines.

Also note that we have one hardware items (grey box) but two component locators, F and F47. You will often find two or more electrical items as part of a single unit. If the F47 switch goes bad, you get a new F47 and F switch as a single unit.

At the top of the wires, the ro/ge (red/yellow) ones, you see a tiny circle. This shows that wire is secured down on a threaded stud. Most of the time you will find this on rather large wires carrying heavy electrical loads. The 3rd wire shown there, a sw wire (black) has a timer crimped to it.

Inside the grey box, again we have thin black lines, these are most likely bus strips, stamped out pieces of metal, not copper wiring. We see a J488, a simple relay in this example. The black box with "2" in it, that number is what relay position the J488 is located in, #2.

Look carefully at how the relay is drawn, it is shown in an open circuit state (switch open). Relays and switches are drawn to show what state they will be in when the car is powered down.... key out of car, all doors closed. The F and F47 above, same thing, powered down, switches not operated. This is important to understand.

And in some cases the wiring diagram will not show the hardware at all (a grey box) but instead just list a terminal. So at the top we have D/50b which is from the ignition switch. Then the wire runs down to the J226 /6, so the J226 module, terminal position #6. From there we come out of the J226 /8, terminal position #8, notice the wire color changes. From there, to T6e/3, so some 6 pin plastic terminal housing, position #3, and finally to the starter. So this bit shows other hardware is involved for that electrical path, but on this wiring diagram, only terminal positions numbers are listed, no further details.

There would be another wiring diagram that shows traditional grey box for the J226 and all of the wiring to and from it.

rucklet · Dec 11, 2014

Very good explanation from you. This can be useful also for many new VW/Audi mechanics, not everyone understands this directly.

NZDubNurd · Dec 12, 2014

Man! I wish I'd seen this some time ago... Took me ages to work out the Current Tracks and some of the details.

Great job!

Thanks :cool:

Davor Sule · Jan 22, 2017

I'm looking for but can't find, how positive connections with 2 or more wires connected together look like (is it weld point or something else)?
For example connection D103:
( there is one power supply wire for 5 or more circuit lines going futher to N75, N18, G70)

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Jack@European_Parts · Jan 22, 2017

D103 Welded connection in harness itself ......follow "a1" and all "Stargates" Think of as "worlds destination" tracks 64,66,19 from "origin worlds" 41,42,43 & proceed to next illustration for observation.

Davor Sule · Jan 22, 2017

Jack@European_Parts said:
D103 Welded connection in harness itself ......follow "a1" and all "Stargates" Think of as "worlds destination" tracks 64,66,19 from "origin worlds" 41,42,43 & proceed to next illustration for observation.

I followed everything. Everything was clear except type of connection. Trace 19 is feeding power supply for these "world destinations".
And I can't understand what you mean exactly.....

Jack@European_Parts · Jan 22, 2017

I followed everything. Everything was clear except type of connection. Trace 19 is feeding power supply for these "world destinations".
And I can't understand what you mean exactly.....

OK where is trace 19 coming from?

Post the WD.........

Davor Sule · Jan 22, 2017

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Davor Sule · Jan 22, 2017

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image search

From these wiring diagrams I can tell that power supply is going over S102 15A fuse and relay J 322, if I'm correct and this is power supply for J359/J360/N75/N18/G70/F47....
only I don't know type of connections and how wires are connected on this D103 connection....
here we have 7 components, every component need power supply, and power supply is coming from 1 wire.... do you know from experience how this type of connection is connected (welded or something else)?

DV52 · Jan 22, 2017

Davor: I have to agree that VW/Audi go out of their way to make their wiring diagrams appear more arcane than they ought to be. I suspect that there is the same element of unnecessary complication in VW's WD that lawyers use in drafting contracts -documents full of useless words that serve no purpose other than to confuse the average reader and to ensure that it's necessary to pay someone else to decipher something that shouldn't need deciphering!

Rant over - Have you looked at Jef's excellent document HERE, which describes how to read WD ? Also, there is a very good PDF document from VW in their "Self Study Program" series titled "How to Read Wiring Diagrams - Symbols, Layout and Navigation" it's SSP- 873003. This is also an excellent resource in trying to understand VW/Audi's arcane nomenclature!. You can download a copy of the SSP HERE, but I've included their explanation regarding your original question

Don

Jack@European_Parts · Jan 22, 2017

Very good post Don /\

From these wiring diagrams I can tell that power supply is going over S102 15A fuse and relay J 322, if I'm correct and this is power supply for J359/J360/N75/N18/G70/F47....
only I don't know type of connections and how wires are connected on this D103 connection....
here we have 7 components, every component need power supply, and power supply is coming from 1 wire.... do you know from experience how this type of connection is connected (welded or something else)?

If you are losing power on a part and everything else tones out you have 3 options.

1.Trace unwrap and locate weld or break........( takes time and patience tone generator recommended ) Best repair because improvements to design can be made or observed if proficient with repairs and forensics of "damage codes" ........"if not"! go new!

2.Replace New Harness module......( takes time and is a PITA ) This repair is new and limits liability.

3.Run overlay ( Cut all wires with issues after loaded and run new tracks to respective point areas to bypass a zone which is verified damaged ) Fastest and cheapest usually and OEM industry standard acceptable.

Davor Sule · Jan 23, 2017

Thank you for recommendations.
I don't have issue with this, I just want to know how it's connected this connection.
I understand Audi wd nomenclature and have been watching Jeff's video and other guides for audi/vw wiring diagrams. I haven't read VW SSP, and thank you for suggestion, I will.

uryah · Mar 18, 2022

Just chiming in to say thank you! I had a fuse go out and this helped me decipher the wiring diagram and was able to identify how the problem happened, tracked to the fuse and replace the fuse in question. What a helpful thread.

gramsca · Aug 14, 2023

Does anyone know what this means? I cannot find an answer for this even from the tons of YouTube videos and forums on wiring diagram tutorials.

Reference to the two wires being conjoined at pin 9.

What it looks like to me is that two wire terminals are connected at one terminal pin. However, I don't think this wouldn't make much sense - because how can two male terminals be joined at a single female pin connector?!
I also cannot find any instance of two wires being joined at one pin in the physical wiring/connectors itself.

It's not marked as a typical "welding point" connection, which means it has to be something different, right?

TTT · Aug 14, 2023

There are terminal pins which allow two conductors to be crimped together.

How to read wiring diagrams

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