Reading VW wiring diagrams

Read this first

The explanation comes from a video series on swapping an Audi RS3 engine into a Golf R¹. The swap itself is on RS3 engine and running-gear swap.

Getting the diagrams

VW and Audi publish factory repair information, including wiring diagrams, through their erWin sites. The owner in the video bought one-day access with printing rights to the US VW and Audi sites, at about US$35 each, and downloaded everything he needed within the 24 hours¹. He says Bentley manuals do not exist for these cars¹.

How to get the same access from the UK or Europe, and at what price, is not covered by the research Unverified.

Page layout

Wire colours and sizes

• Wire colours are German abbreviations; for example "ge" is yellow¹.
• The number beside a wire is its cross-section in mm²¹.
• Brown wires are usually grounds, but not always: check the diagram¹.

Track numbers

Track numbers run along the bottom of each page. A boxed number on a wire is the track where that wire continues, so you can jump to it without following the line¹.

Ground points

A wire that ends at the bottom of the page with a number in a circle goes to a ground point. The ground points are listed by number: for example, 12 is the ground connection in the engine compartment, left. On the Golf the owner took that to be the ground behind the battery on the bulkhead¹.

Connector notation

On a large connector the pin numbers may be printed only at the ends of each row. On the 91-pin ECU plug the six large cavities are the powers and grounds¹.

Worked example: exhaust flap J945

Following one component through the Golf diagrams¹:

1. The flap has a 3-pin connector: pin 1 is the signal, pin 2 is terminal 87a (switched power) and pin 3 is ground¹.
2. Ground runs through a splice in the rear harness to a ground point in the left rear wheel housing, which tells you this is the left rear flap¹.
3. The signal wire (violet) runs through the 17-pin junction TIUL (interior, lower left, by the footrest) to ECU pin T91/10¹.
4. Power comes from positive connection B350, fed by fuse SB10. The same fuse also feeds V488 (heater support pump) and N205 (camshaft adjuster)¹.

The fuse number differs between the sources: the video reads SB10, while the same owner's written notes put the Golf's exhaust flaps on SB9 (and the RS3's on SB5) Sources differ^1,2. Check the diagram for your own car.

Depinning and repinning

Moving a terminal from one cavity or connector to another, without cutting the wire¹:

1. Remove the secondary lock (a purple slide on the connectors in the video).
2. Release the primary lock with a depinning tool, which pushes in the retaining tabs, and pull the wire out.
3. Push the terminal into its new cavity until it clicks.
4. Refit the secondary lock.

Count cavities carefully where numbers are only printed at the ends; the owner miscounted three or four times on a 91-pin plug¹. Label every wire, for example with masking-tape flags and a marker¹. After moving wires to match a different control unit, the colours will no longer match that unit's diagram, but the positions will be right¹.

Splicing

Where a wire cannot be moved, cut and splice it. The owner used crimp butt connectors with heat shrink, and sealed them only after testing. He says this matches VW and Audi wiring repair practice Unverified¹. A splice is also needed where a wire is the wrong size for its new cavity: in the same swap a 0.35 mm² wire and a 1.0 mm² wire had to be joined because the thicker one would not fit².

Tips

• Study the diagrams before starting; for a whole engine harness the owner needed about a week of evenings¹.
• Document every pin in a spreadsheet: source pin, destination pin, colour and route^1,2.
• Go slowly and recheck about every ten wires¹.
• No twist-on connectors, and cut cable ties flush¹.