Introduction

First, you will need two "T10" bulb sockets. I used a simple rubber push-in type that require only a round 9/16" hole for installation.

I found a set of 10 on AliExpress for $2.99 US. You can see the ones I purchased at THIS LINK.

Product Name: T10 Light Socket
Material: Plastic
Socket Type: T10
Color: Black
Wire Length: 13cm/5.1"
Package Content: 10 x T10 Light Socket
Socket Size: 20 x 25mm /0.8" x 1"(D*L)

You will also need a pair of red LED bulbs. They must be LED, you cannot mix the stock LED CHMSL and incandescent bulbs in the same circuit.

I bought a pair from AliExpress for $6.74 US from THIS LINK.

They are sold in different colours, so make sure to pick red (picture at left and the next two pictures are of the white light variety).

The specs are as follows:

• Powered by 10 super bright 3030 high power LED lights
• 3000k red color
• CAN-bus Error Free design (works with most European cars with no warning message on dashboard, no flickering/not lighting up issue)
• 500 Lumen 
• LEDs power:1.5w
• Working voltage: 12V-24V D
• working temperature:-40°C- 105°C

Finally you will need an LED flashing module.

I bought this one from AliExpress for $2.56 US from THIS LINK.

Specs are:

• Rated input voltage: BATTERY12--24V
• Rated input current: 0.8A to 1.2A
• Rated power: 10W to 15W
• Working temperature: -40 to 50 degrees Celsius
• Storage temperature: -50 to 80 degrees Celsius
• Size: 4.8*2.2*1.3cm
• Wire length: Approx. 15cm

For scale.

It's actually quite small, and it comes with a little piece of double-sided adhesive tape to secure it in place in your chosen location.

Wiring is very simple, you simply connect the IN and OUT positive and negative wires in0line with whatever LEDs you want to flash.

For example, if you didn't want to add the two auxiliary LED bulbs that I did (or if you have rear fog lights) you could still use the flasher unit to flash the LED CHMSL.

To do so, remove the plastic pins securing the cover on the underside of the trunk lid to expose the wiring.

The wires for the CHMSL are indicated here by the blue arrow.

The green wire is the (+) and the black is the (-).

To wire in the flasher you cut both wires, then:

• Connect the green wire coming from the white connector to the red wire on the IN side of the flasher.
• Connect the black wire coming from the white connector to the black wire on the IN side of the flasher.
• Connect the red wire on the OUT side of the flasher to the green wire going to the CHMSL.
• Connect the black wire on the OUT side of the flasher to the black wire going to the CHMSL.

However, if you're adding the extra brake light LED bulbs, the next step is to remove the bottom and left side trunk liners.

Remove the two push-pins at the forward edge of the trunk by prying them up with a small pick or screwdriver. These two are different from all the rest (having no centre locking pin), so remember where they go.

Next, remove the remaining 6 pins from the left side.

There is one behind the rear plastic panel (location indicated by the red arrow) which you have to pry the plastic panel forward to access.

With all the pins removed, remove the bottom liner and then the left side one. The left one takes a bit of wiggling to get out (and back in).

Before going any further, disconnect the negative wire from the battery, and press the brake pedal once to ensure no current in any of the car's circuits.

With the left side liner removed, we can see the connector that has the wire that powers the CHMSL.

It's the red wire. This is the one we will tap into to power the flasher module.

But before we get to the wiring, we need to install the two new bulb sockets in the lower light housing.

Time to crawl under the car from the rear. You can do this without jacking the car up, but you'll have more room and be more comfortable if you do raise the rear end a bit.

It's advisable to remove the light housing from the vehicle for the modification as it's really cramped under there.

The blue arrows show the locations where we're going to be installing the new LED bulbs, and the red arrow shows the underside of the grommet through which we're going to run the new wires.

Before we remove the screws and take out the assembly, there are a few things we must disconnect.

From left to right in this pic, remove:

• The reverse lamp socket by turning counter-clockwise a 1/4 turn and pulling out.
• Wiring harness clip, by squeezing the little tabs and pushing it up through the slot.
• Electrical connector by squeezing and pulling out.

With all the disconnections made, remove the 6 phillips-head mounting screws.

The two at the top are not shown in this pic, but their approximate locations are shown by the top two blue arrows. They're not too hard to reach, but my camera would not fit up there to get a good shot of them.

With the 6 screws removed, carefully wiggle the housing out of the car.

I used a rotary tool with an abrasive bit to grind them away.

With patience and care you could use a sharp utility knife or a small hacksaw blade or even a small file.

I began the drilling in this position, but before breaking through the plastic all the way, I held the housing the other way up to finish the drilling in order to minimize the amount of plastic drilling debris that falls into the light housing.

If some does get into the housing, blow/vacuum/shale it out before continuing.

Next, connect the positive and negative wires from both sockets together and then to each add 48" (4 feet) of additional wire. I used red and black 16 gauge because that's what I had on hand. The LED bulb current draw is so small that almost any gauge will do...the factory wires are tiny...something like 22 gauge I think.

I chose to solder the wires together and cover them with heat-shrink tubing and then taping them with electrical tape.

You could use some other method, like crimp-on fittings, but whatever you do, make sure the connections are secure and weatherproof.

This is the grommet into which I cut a small slit with a sharp utility knife so I could run the wires from the new sockets into the trunk of the car. I ran the wires through the grommet and then took the assembly, wires, and grommet under the car, fitted the assembly into place, re-installed the 6 mounting screws, re-connected everything I had previously disconnected, and then pushed the grommet into place from underneath the car.

Then I used a few zip ties to keep the wires secure and tidy.

Here's the finished product from under the car.

If I was to critique my own work I would say I should have taped the new wires a little further (red arrow) and the wires to the right socket are a little short/strained.

Finished under the car, it's time to complete the wiring in the trunk.

First I added some silicone sealant to the grommet where the wires come through to keep it water-tight.

Here's the run down on the wiring:

A - factory red wire going TO the CHMSL.
B - factory red wire coming from the brake pedal switch.
C - Flasher IN Positive (+) wire.
D - Flasher IN Ground (-) wire.
E - Flasher OUT Ground (-) wire.
F - Flasher OUT Positive (+) wire.
G - New lower-brake light Positive (+) wire.
H - New lower-brake light Ground (-) wire.

Make the connections as follows:

F to G and A

E to H

C to B

D to chassis ground