Last weekend I received a new CHMSL kit from my supplier. This is the updated kit which does not require you to remove the back window while replacing the light. The procedure was recommended to be performed only by professionals, but I opted to try myself and save myself about $1000.00 doing it. Even when I called the Bentley dealer I was warned, I would break the glass or light while attempting installing the light. Now after the fact, I am not sure why this is so difficult. It took me about 3 hours to perform and really wasn't too difficult. I could event done it faster, if I never documented everything I did. Also Want to thank @BentleyTech for re-iterating the R&R process for me.


When you order the CHMSL ( Central High Mounted Stop Light) kit you will also receive a adhesive pad and obscuration strip. The kit cost anywhere from $400-$500 depending where you get it. Below is what the light looks like.




First thing I did was to connect the light to power and see that it works.


Inspecting the old light assembly, you can see how it has a lip which extends under the rear window glass. if you look closely in the picture below, you can actually see this lip extending under the glass.





This lip has to be cut off so the old light can be removed. There are many ways to remove this lip. I first thought about using a Dremel, but opted for an used angle saw I acquired at Harbor Freight tools for $8.00. Before I started to saw off the lip I used some masking tape to protect the glass side, just in case. After that I simply just sawed off the lip like below:





While sawing off the lip you can feel when the blade is cutting the plastic and starting to hit the metal. You cannot avoid hitting the metal, but do not saw through it.


After the lip is cut off, you should be able to lift off the old light assembly from the clips holding it in place using a dent puller with a screw attachment.




My dent puller is maybe a little too big for the job, but nevertheless, it worked just perfectly. First simply drill a pilot hole then attach the dent puller and carefully pull up the old assembly like below:





I was lucky and only had to use the dent puller once to lift the brake light off the clips. You may have to use the puller two or three times (Once per clip) to be able to lift off the whole light.





After removing the Light assembly remove the remainder of the lip using a small screw driver like so:





You can see in the picture above how my angle saw scratched the paint protecting the body. We have to re-paint this or else have a huge rust problem in the near future.





First give everything a really good cleaning using only water. Do not use any car detailing chemicals, since many of them contain oils which makes new paint bubble when applying it. Get some good primer/sealer and a few q-tips and apply it to the bare metal scratches. if you bought a spray can like I did, just spray enough in a cup so you can dip the q-tips in it. Apply like shown:





Now the real fun is going to start, which is hooking up the electrical connectors to the new light. This will require you to remove some interior panels so you can gain access to the brake connector. My car is a left hand steered car, so the procedure may differ on a right hand steered car. Open the Left rear window to ease access. Pull out the bottom rear cushion by simply unsnapping it. After the bottom cushion is removed, you will see a nut on the bottom of the rear cushion holding it in place. Remove it and push the rear cushion downward to unlatch it. Now you should have access to the left shelf and upper D-pillar:





You should be able to remove both the shelf and D-Pillar cover as one piece. Unsnap the plastic cover at the back of the side window. Push out the ABS plastic logo and unscrew the nut behind it, undo the rear seat belt bracket, then finally as the arrow on the left shows unscrew the screw holding the shelf cover. When working with airbags make sure the fuses are removed or the battery disconnected. We do not want to set off any airbags by accident.


Now it should look something like this:





This should be enough to access the brake wiring from the inside by pulling back the (blue leather) left upper headliner side or whatever it is called.





The picture above illustrates the brake light wire connecting to the fly strip which is sandwiched between the rear glass and car body. This is seen by pulling back the top side cover.

After the brake connector is exposed, it is time to start installing the new brake light. I opted to cut the connector off the new light and then solder it back when the wires are pulled under the glass.

This is probably the hardest part of the job pushing the new wires through the glass inside the car. First you have to dig out the sealant. Just enough for the wires to come through. I use a piece of bailing wire folded over the electrical wires, so I could easily push it through the sealant as shown:





After the wires are pushed through, I re-soldered the connector to the wires, connected it, and made sure again the light was working. Re-seal the hole you created using the supplied adhesive pad.





Just roll it up and seal the crack you dug out for the wires.




Then attach the obscuration strip like so:





Carefully position the light and attach it into the clips. Make sure it is aligned properly while pressing it into the clips. You cannot easily remove the light again after it is mounted. Now all you have to do is to reassemble the interior and you are done. This should take less than three hours to perform and possibly save you $1000 or more.





All Done

 

Excellent!! This is a common problem and your explanation is detailed. Thank you for the effort you have put into documenting this procedure. We are all enriched.

 

Wow, huge thanks for posting this as it is indeed a very common problem on older cars.

 

Meh.....
Looks like I really screwed up the topic title an cannot correct it. Should read:

3rd Brake Light CHMSL Replacement - HowTo

 

Just curious what's the purpose of the obscuration strip since there seems that there wasn't one there before.

 

Its cosmetic to obscure the the primer etc from replacing the old light. Hence the name obscuration strip......

This is my guess.....

Cheers,

Zaos

 

That's pretty awesome.

I know my garage broke the corner of the screen in the first 5 minutes, and had to foot the 4k bill, so all credit to you.

 

Yup, Most likely tried to pry off the light using a screwdriver or something, rather than using the dent-puller.


Cheers,


~ZaOs~

 

It is also possible to remove the light without cutting. It can be pryed up quite easily with a plastic tool.

 

Some may be easier to pry, some may not. Depends how tight the light is clipped in and the version of the light assembly. The new kind has no lip. This is when you make the decision risking cracking the glass or not.

 

just got mine replace at GTmotorworks in south florida by marcus in 1 day for $1200

 

Has anyone tried cutting the lip with a hot knife? Im thinking this will be safer than trying to cut the lip.

 

 

You can cut the strip with a regular construction knife(box cutter) by going over it a few times. If you use a saw there is a chance of shattering the rear window.

 

I wanted to thank you @Zaos for this writeup. It was super helpful!

I just finished replacing my 3rd brake light. The hardest part with pulling the wire thru the window sealant, but I managed to do it without shattering the back window!

And @Glass Dome , it won't be possible to do that because the old light used a ribbon to pass thru the window sealant. There isn't a way to splice it and even if there was it would be hard to put the joint in the space under the light. The interior disassembly isn't that bad. Just remember to remove the fuse for the airbags before you start.