A3.BlogSpot.com_Audi_A3_US_Trailer-Wiring_Install_DIY.pdf

TRAILER LIGHTING CONVERTER INSTALLATION

AUDI A3 (8P SPORTBACK), US MODEL, 2006+

The Audi A3 is part of a new generation in automotive electronics, which brings both a new ability to customize it easily as well as new

issues to take into account when tapping into or modifying the electrical system.

With modern technology, everything in the A3 is handled through one of several onboard computer systems. Every switch and device

(including light bulbs) is part of the Controller Area Network (CAN) which runs throughout the car. This means that many features can

be modiﬁed by altering the settings of the CAN

system computer. Changing these settings can be

accomplished with a commercially-available soft-

ware program and interface cable, and is some-

thing frequently done by Audi enthusiasts.

These instructions will guide you through installing

a trailer lighting interface on the Audi A3's variable-

voltage lighting system in a problem-free manner.

No computer settings will need to be changed, and

following these instructions ensures that if any of

the settings are changed at a later date, the trailer

interface will be unaffected.

Here's a comparison of "the old way" vs. how the

A3’s lighting system behaves:

The old way: There were separate bulbs (or sepa-

rate ﬁlaments within a single bulb) for 'tail' and

'brake' lights. The difference in brightness be-

tween 'tail' and 'brake' was due to the wattage of

the bulbs; they both received about 12 volts; and

they were hard-wired to perform only whichever

function they were intended for.

How the A3 works: In addition to dedicated turn signals and backup (reverse) lights, the Audi A3 has three bulbs on each side that

can act as tail and/or brake and/or 'rear fog' lights. These bulbs are all of the same type, and only have one ﬁlament each. The com-

puter applies reduced voltage to one or more bulbs on each side, making them glow at 24% of their maximum brightness to act as tail

lights. Which bulbs are activated, and the percentage of brightness, are dependent on the settings in the car's computer. When you

step on the brake pedal, the computer increases the tail light voltage to make the bulbs glow at 100% of their maximum brightness to

act as brake lights. Again, which of the bulbs are affected is dependent on the computer settings. The behaviour can be changed by

altering the computer settings, no re-wiring needed. A3's sold in other countries have the taillights conﬁgured differently to meet local

regulations as necessary.

Unfortunately, this variable-voltage system does not work properly for US trailer wiring - trailer taillights expect to receive about 12

volts, not 3.5 volts - and the fact that the 'brake' and 'tail' lights on the car can be re-arranged in software means that those wires

cannot be relied upon to always behave in the same way. There is a simple solution to this: Use things on the car that will always

behave as desired. This means using the center, high-mount brake light on the car for ‘brake’, and using the license-plate lights for

‘tail’. Both of these circuits only have 'off' and 'on' states (not variable-voltage), and both only have one purpose and cannot be re-

programmed. The converter speciﬁed puts no load on the lighting circuits, they are only used for sensing the voltage present.

Enjoy towing safely with your Audi A3!

STEP-BY-STEP INSTRUCTIONS

ALL MATERIALS AND TOOLS LISTED

COMPLETELY INVISIBLE WHEN INSTALLED

Audi A3 (8P Sportback) US Trailer Lighting Converter Installation

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WIRING CONVERTER

The converter used for the A3 is the

Hopkins Manufacturing (Hoppy) 46365 .

This model is speciﬁed because:

The packaging includes:

The converter box itself has the trailer

harness ribbon & 4-ﬂat connector at-

tached to one side, and 6 hookup wires

on the other side:

• A length of red wire for +12V power

• Some small zip-ties

It isolates the load of the trailer light-

ing from the vehicle lighting circuits.

The connections to the wiring of the

vehicle lights are for sensing voltage

only. A separate, dedicated power

source connection provides power

for the trailer lights.

• LARGER RED: +12V

• A package of dielectric grease.

• GREEN: Sense wire for Right Turn

Signal

• 4 tap-splices (1 will be used for the

power line; the other 3 will not be used

- they are too large for the rest of the

vehicle wiring connections)

• SMALLER RED: Sense wire for Brake

Light

It protects the vehicle from short-

circuits in the trailer lighting.

• A screw (will not be used)

• YELLOW: Sense wire for Left Turn

Signal

• An in-line fuse (will not be used)

It will not interfere with the vehicle’s

‘bulb failure’ diagnostics

• BROWN: Sense wire for Tail Lamp

• WHITE: Ground

It has been tested and found to work

properly when installed as described

in these instructions.

Audi A3 (8P Sportback) US Trailer Lighting Converter Installation

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TOOLS & MATERIALS

All of the tools and materials listed below

can be obtained at hardware or home-

improvement stores.

A DC voltmeter is highly recommeded for

verifying that the correct voltage is being

provided to the trailer lighting connector.

The use of a wire crimping tool for secur-

ing butt-splices is highly recommended.

Using other tools to crimp a splice may

result in poor connections or damage to

the wire, splice or insulation.

QUANTITY

TOOLS & MATERIALS NEEDED

THESE ITEMS ARE IN ADDITION TO THE MATERIALS SUPPLIED IN THE

HOPKINS 46365 CONVERTER PACKAGING

1 Roll

18 gauge primary wire (green)

18-22 gauge tap splices (no larger, since the vehicle wiring is very

small gauge)

18-22 gauge butt splices

1 Tube

Goop™ brand clear silicone adhesive/sealant

1 Roll

Electrical tape

1 Package

Standard-size (e.g. 7”) zip-ties

1 Package

Mini zip-ties

Torx T-25 driver

Pliers

10mm socket & driver (deep socket recommended)

Wire crimp/cut tool

Razor blade or sharp knife

12V test light, and/or voltmeter (recommended)

Audi A3 (8P Sportback) US Trailer Lighting Converter Installation

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PREPARING THE CARGO AREA

• Open the rear hatch

The crosspanel (black plastic trim) along

the edge of the hatch opening must be

removed. Figures ‘A’ and ‘B’ above indi-

cate the locations to grasp::

Figure ‘C’ above shows the cargo area

with the crosspanel removed. The

painted metal that is now visible is a hol-

low channel. As part of this installation,

2 wires will be run across from the left to

the right side (for right turn signal sense,

and +12V) through this channel.

• Remove the cargo area cover (shelf)

• Remove the cargo net (if present) & any

rubber cargo liner (if present)

• Grasp it above the cargo net hooks as

shown in ‘B’ above, and pull straight

upward. Four clips will pop out of their

spots loudly as it comes up.

• Fold down both rear seatbacks

• Remove the carpeted ﬂoor panel which

covers the spare

• Pull evenly on both left and right sides

at once, not at an angle.

Note how the gasket originally overlaps

the crosspanel, and the crosspanel pulls

out from under it. When the crosspanel

is reinstalled later, the gasket will need to

be returned to its original position over-

lapping, not pinched by, the crosspanel.

Audi A3 (8P Sportback) US Trailer Lighting Converter Installation

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LEFT SIDE: OPENING THE INTERIOR SIDE PANELS

clips are loosened, the short wiring

harness going to the cargo area light

will be visible.

READ THIS ENTIRE STEP BEFORE

PROCEEDING:

• Use a T-25 driver to remove the torx

screw from the left side panel as

shown in Figure ‘A’. (Also remove the

corresponding torx screw from the

right side panel at this time.) Label

these, and set them aside.

• IMPORTANT: See Figure ‘D’ above.

Carefully press on the clips to pop the

cargo area light outward (from behind),

then feed it through the opening so

that the wiring is no longer limiting the

movement of the side panel. (This is

easier than trying to unplug the electri-

cal connector from the light while the

light is still in place.)

• Grasp the lower rigid part of the left

side panel as shown, and pull outward

(towards the right side of the car) as

shown in Figure ‘B’. This will pop out

the clips holding it in, and begin to peel

it from behind the hatch gasket.

The side panels will not be completely

removed, just opened enough to reach

the installation areas.

• IMPORTANT: See Figure ‘C’ above.

As you loosen and pull out the side

panel, there are some clips along the

top where it meets the upholstery. Be

careful loosening these. Once those

Audi A3 (8P Sportback) US Trailer Lighting Converter Installation

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