Non-OEM Earth/Ground Wire Installation -

Hardware:

1.) 2-3 meters of automotive Ø 2.5mm / 14 AWG ground wire

• Brown is the standard VAG wire color for earth/ground wire​

• Be sure this is solid copper strand, not CCA (Copper Clad Aluminum). Post here on why that is important!​

2.) 2.5mm/14 AWG Ring connectors (x8)

• Note - the ID of the ring connectors should match the diameter of the bolts.​

3.) 2.5mm/14 AWG Male bullet/spade connectors (x2)
4.) 2.5mm/14 AWG Female bullet/spade connectors (x2)
5.) Good pair of wire crimping pliers
6.) M5/M6 stainless steel flange hex-head bolts (x4)

• M5/M6 Washers (x4)​

• M5/M6 Nyloc nuts (x4)​

7.) Automotive electrical cloth tape
8.) Heat shrink tubing
9.) New tail light bulbs: P21W (x2) and W16W (x3)

There are two easy to access ground points inside the trunk area; one on the left side near the location for the Bose Amp, and another in about the same spot on the right side near the battery. You should use these point located inside the trunk rather than connecting to external earth/ground point to avoid corrosion.

Any good automotive electrical shop or car stereo shop should be able to sell you a couple of meters of 2.5-diameter ground wire. Brown is the standard VAG color for earth/ground.

This project will require you to make three different wires for each tail light assembly:

1.) The internal Ground Plane Jump Wire which connects the upper and lower ground planes together inside the tail light assembly.

2.) The Tail Light Ground Wire which connects the tail light to the Primary Ground Wire.

3.) The Primary Ground Wire which runs from the tail light location, through the rubber grommet and into the boot/trunk where it will be terminated at a chassis ground point.

Shown below, hardware and ring terminal on Ø2.5mm brown earth wire -

When securing the terminal with the bolt, note the orientation so the ring terminal is held flat against the ground plane when secured -

Start by removing the tail lights from the vehicle and disassembling the inner and outer tail light assemblies.

Once you have the inner and outer tail light assemblies separated, it's much easier to work with the internal assembly if you also remove the two large P21W bulbs. You can leave the three smaller ones in place, just be careful while you are working with it. But since you have it all taken apart anyway, this is a good time to remove all the bulbs and then replace them during final assembly.

1. Drilling Holes

1.1 Drill an M5/M6 hole through the grey plastic housing (from the inside) close to the edges of both the upper and lower ground planes (GP).

It is important that the hole is as close to the edge of the GP as possible since the top of the screw will make full contact the GP once it's secured in place.

Lower GP and Upper GP hole locations -

Detail of Lower GP location left, Upper GP location right -

2. Connecting the Upper and Lower GPs

2.1 Ground Plane Jumper Wire -

• Cut two lengths of wire, 18cm / 7" long (one for each tail light).
• Crimp two ring terminals on each end and secure with heat shrink tubing.
• This wire will connect the upper and lower GPs inside the tail light assembly.

2.2 Tail Light Ground Wire -

• Cut two length of wire, 18cm / 7" long (one for each tail light).
• Crimp a ring terminal on one end and a bullet or spade terminal on the other.
• This wire will be connected to the outside of the tail light assembly and will connect to the primary ground wire inside the boot/trunk.

2.3 Position one of the GP jumper wire ring terminals over the upper ground plane position and insert the bolt through the hole.

2.4 Fasten the washer and nut on the opposite side and secure in place.

• CAUTION - Be sure no part of the terminal comes in contact with other circuit planes as this could potentially cause a short circuit.​

• Do not over tighten the nut or you may crack the plastic.​

2.5 Form the wire against the back of the assembly as shown, and position the other ring terminal above the hole near the lower ground plane. The wire should be rigid enough that it stays in place and does not interfere the outer tail light assembly.

Connection to the Upper GP -

2.6 Insert the bolt through ring terminal and the hole.

2.7 Place the washer on the other side of the protruding bolt.

2.8 Place the ring terminal of the Tail Light Ground Wire through bolt,

• Check the position so it is aligned with the OEM connection.​

2.9 Secure the lock-nut.

• CAUTION - Do not over tighten the nut or you may crack the plastic.​

2.10 Reassemble the tail light assemblies.

• You might want to replace all the bulbs before you finish putting the tail light assembly back together.​

This section is now complete. Repeat this process for the other tail light assembly.

Jumper connection at the Lower GP -

Jumper connection across the upper and lower GPs -

Outside of the assembly, place the washer first, then the ring terminal and then secure the Nyloc nut -

Outside of the assembly, the Tail Light Ground Wire is secured to the lower GP bolt. The upper ground connection Nyloc nut and washer can be seen in the lower right -

The tail light has been reassembled and is ready to be put back into the vehicle. Note the alignment of the Tail Light Ground Wire relative to the connector on the tail light -

 

Connecting the Tail Light Assembly to the Vehicle Earth Point -

With the internal Ground Plane Jump Wire and the Tail Light Ground Wire in place, the next step is to make a Primary Ground Wire. This will go from the tail light location, through the rubber grommet and into the boot/trunk where it will be terminated at a chassis ground point.

The trunk floor deck, both trunk side panels and the foam tool inserts will need to be removed before you can route and connect the primary ground wires.

3. Installing the the Primary Ground Wire -

3.1 Cut two lengths of Ø2.5mm wire 1-meter long. One for each tail light.

• Note - for the purpose of this demonstration, I used a green-yellow wire so it's easier to see in the pictures.​

3.2 Carefully remove the rubber grommet from the metal work and remove the existing electrical cloth tape from the grommet and wires.

• Notice how this was done at the factory as you will be replacing this with new tape.​

3.3 Pass one end of the Primary Ground Wire through the grommet from the inside to the outside where the tail light resides.

• The end of the wire should be blunt cut, not stripped. There should be no protruding wire strands to catch on the rubber grommet.​

• A simple lubricant such as dish soap applied to the end of the wire can to help make it easier to pass the wire through the grommet.​

3.4 Pull enough wire through the grommet to match the length of the existing tail light connector wires so both can be easily connected /disconnected when necessary.

3.5 The remaining wire should be routed back into the boot/trunk.

3.6 Wrap the ground wire and tail light connector wires to the grommet with electrical cloth tape to secure them in place.

3.7 Carefully reinstall the grommet into the metal work.

• Be sure the grommet it is fitted correctly or water can get into the trunk.​

3.8 Crimp the spade/bullet terminal on the end of the wire near the tail light.

3.9 Inside the boot/trunk, route the wire to the closest ground point and cut to length.

• See images below for ground points.​

3.10 Crimp a ring terminal onto the end of the wire and secure the ring terminal to the ground point.

• To keep the wire from moving around or rattling against the metal work, secure it to any other cable harnesses in the area with small cable ties.​

3.11 Connect the OEM connector to the tail light assembly.

3.12 Connect the Tail Light Ground Wire to the Primary Ground Wire.

3.13 Re-install the tail light into the vehicle.

4. Testing

4.1 Turn on the tail lights, indicator and reverse lights. Check the brake light too.

4.2 Verify all bulbs illuminate and no warning messages are displayed on the DIS.

Job done!

Both the OEM wiring harness and connector with the Primary Ground Wire pass through the grommet. In this image, the electrical tape has not yet been applied -

Location of the right side chassis ground located aft of the battery -

Location of the left side chassis ground located aft and below the Bose Amp -