Water leaking in rear of cab - brake light?

ember1205 · November 7, 2020

2015 CCSB 4x4, 77,000 miles - bought it new in August of 2015. I haven't had many issues crop up with the truck until lately. I am getting some water leaking into the rear of the cab (drips down the rear window, no slider just single piece of glass) and I've also noticed condensation inside of the third brake light.

If you have had a leak AND FIXED IT YOURSELF... How did you determine it was the brake light or did you just assume it was? What did you do to address the issue - replace the assembly or something else? What sort of cost is there for the light assembly or whatever parts you used?

If you had the issue and PAID THE DEALER to fix it, how much of an expense might that end up running?

I'm trying to decide if I should tackle it myself or hand over too much money to the stealership. Also, there's a very small chance that I may trade it towards a new one, but that's a big "it depends" sort of thing right now.

rav3 · November 7, 2020

I will assume that your seal is bad on the high mount brake/cargo light. I have viewed several videos on youtube concerning this.

Removing the light is not difficult. @ screws & you can pull it out. The issue would be is it the foam seal or is the plastic lens broke. I do not endorse the method used in this video, that's up to you. I would think it would make it difficult to remove in the future. Just saying.... Hope this helps you see how to remove the light. Don't break it like he did.

https://youtu.be/Ft3-aVCLoGk

Edited November 7, 2020 by rav3

ember1205 · November 7, 2020

Thank you, @rav3. Helpful details in the video, especially the pieces about "don't damage your light"... lol

I don't know that I agree with the specifics of their fix, but the main gist of it makes sense. I've ordered a gasket and will tackle it in the next couple of days. I do not believe the lens is broken, but I won't know for certain until I remove it from the truck (and plan to do that only once when I intend to replace the gasket).

JimCost2014 · November 7, 2020

Just replace the light, your truck is 5 years old and you live in a pretty harsh environment with the huge temperature swings from summer to winter.

It would be a lot safer if you have doubts about the existing light, and would give you some peace of mind with winter coming. They are not very expensive and easy to replace.

ember1205 · November 7, 2020

18 minutes ago, JimCost2014 said:

Just replace the light, your truck is 5 years old and you live in a pretty harsh environment with the huge temperature swings from summer to winter.

It would be a lot safer if you have doubts about the existing light, and would give you some peace of mind with winter coming. They are not very expensive and easy to replace.

The light is about $120. A new gasket is $15. Effort is the same.

I don't believe there's anything wrong with the light, so I'm willing to try the gasket first and see what happens.

JimCost2014 · November 7, 2020

9 minutes ago, ember1205 said:

The light is about $120. A new gasket is $15. Effort is the same.

I don't believe there's anything wrong with the light, so I'm willing to try the gasket first and see what happens.

Just make sure everything is as clean as possible on the truck, no dirt, silicone, anything that might cause a void.

Run you finger along the whole edge of the light to make sure there is no warpage, chips, or anything that might let water in.

Good luck, water leaks are a PITA.

OffTheAir · November 7, 2020

Yeah, I had to tackle this problem this previous winter. It started with just a quick look at the headliner one day; mine was stained real bad. After that, began to notice water spots on the inside of the rear window. I initially didn't think it was the brake light, but knowing it was a common problem thanks to this forum I pulled it out and sure enough there was a pool of water inside the thing, and pretty bad dirt buildup above the cabin. Just looking on the inside, it was easy to tell that it was the gasket that was defective.

Luckily, there's all sorts of options since this is such a desirable solution as opposed to just replacing the whole assembly (mine was totally fine, save for the gasket). I ended up buying a new one from VIPMOTOZ on Amazon for $7.99 (https://www.amazon.com/VIPMOTOZ-Replacement-2014-2018-Silverado-Thickness/dp/B07S42JG26/ref=sr_1_6?dchild=1&keywords=2014+gmc+sierra+third+brake+light+gasket&qid=1604789932&replacementKeywords=third+brake+light+gasket&sr=8-6&vehicle=2014-48-548------------&vehicleName=2014+GMC+Sierra+1500).

Very thick seal and it does a good job repelling water, just discard the old one and put this in its place. I've also seen people add an extra layer of silicone on top of this around the brake light, but I really didn't think it was necessary. I didn't do a very good job and was afraid of braking the light, so I ended up paying this guy at my local shop like $20 to swap the gaskets and ensure fitment was right, since he does them all the time. Overall, very happy with the results! I think you'll have no problem tackling this job, and when you're done you'll never have to worry about it leaking again

ember1205 · November 8, 2020

17 hours ago, JimCost2014 said:

Just make sure everything is as clean as possible on the truck, no dirt, silicone, anything that might cause a void.

Run you finger along the whole edge of the light to make sure there is no warpage, chips, or anything that might let water in.

Good luck, water leaks are a PITA.

Agree all around. I am planning to tackle this today... I just need to pick up some thread sealant for the screws for when they go back in, although I have to wonder why they used thread sealant at all - the waterproofing really should happen directly under the head of the screw and not along the threads. I may just put a touch of sealant or silicone there instead.

ember1205 · November 8, 2020

16 hours ago, OffTheAir said:

Yeah, I had to tackle this problem this previous winter. It started with just a quick look at the headliner one day; mine was stained real bad. After that, began to notice water spots on the inside of the rear window. I initially didn't think it was the brake light, but knowing it was a common problem thanks to this forum I pulled it out and sure enough there was a pool of water inside the thing, and pretty bad dirt buildup above the cabin. Just looking on the inside, it was easy to tell that it was the gasket that was defective.

Luckily, there's all sorts of options since this is such a desirable solution as opposed to just replacing the whole assembly (mine was totally fine, save for the gasket). I ended up buying a new one from VIPMOTOZ on Amazon for $7.99 (https://www.amazon.com/VIPMOTOZ-Replacement-2014-2018-Silverado-Thickness/dp/B07S42JG26/ref=sr_1_6?dchild=1&keywords=2014+gmc+sierra+third+brake+light+gasket&qid=1604789932&replacementKeywords=third+brake+light+gasket&sr=8-6&vehicle=2014-48-548------------&vehicleName=2014+GMC+Sierra+1500).

Very thick seal and it does a good job repelling water, just discard the old one and put this in its place. I've also seen people add an extra layer of silicone on top of this around the brake light, but I really didn't think it was necessary. I didn't do a very good job and was afraid of braking the light, so I ended up paying this guy at my local shop like $20 to swap the gaskets and ensure fitment was right, since he does them all the time. Overall, very happy with the results! I think you'll have no problem tackling this job, and when you're done you'll never have to worry about it leaking again

Thanks. I have a gasket coming today and will be tackling it myself. I am usually pretty capable with this sort of stuff. If I break the assembly, it's on me to correct it.