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2003 chevy trailblazer_lt_ext
214 Posts
Discussion Starter · #1 ·
This was completed on a 2003 Trailblazer EXT LT

Proceed at own risk!!!
The Directions below were done with the parts and tools below. If you decide to use a different part or tool, these directions may not work.

Parts and Tools needed
• Phillips Screw Driver (shorty; needed to remove 3rd Brake Light),
• Miniature Flat Head Screw Driver,
• Dremel/Rotozip with drill bit
• Razor Blade (New Blade)
• Wire Cutters
• Wire Strippers
• Soldering Iron
• Solder
• PVC Glue or adhesive product
• PVC Glue Primer (only needed for PVC Glue)
• Metal Straight Edge (if using plexi glass)
• Duct Tape and/or Clamps
• Ruler or Tape Measure
• Air Compressor with Nozzle (blow out debris from inside light), Compressed Air should work the same but you may need more then 1 can.
• Standard Flat File

• 9” LED 2 Pack (Advanced Auto Parts)
• 3rd Brake Light
• Silicone or Gasket Sealer
• Acrylic sheet or similar shaped “bracket” (19” minimum recommended length)
• Extra Wire (20” should be sufficient / 20-22GA)

1. Open the whole tailgate (If in a garage watch out for overhead clearance)
2. Pull weather stripping down from top center by the rear dome light. This should expose the space between the roof fabric and the top of the truck.
3. You may be able to see the connector that goes to the 3rd Brake Light. If not, lightly pull down roof fabric, it should just be lying on top of the roof fabric.
4. Take the Miniature Screw Driver and gently pry up the top of the female connector, then pull the male side to free the Brake Light connector.
5. Push/Pull the rubber sealer/wire up through the top of the body.
6. Lower the tailgate, unlatch the window from the tailgate. Do NOT open the window if in a garage with low clearance. If not in a garage or if there is enough clearance, you can open the window, then lift the tailgate back up.
7. Unhook the wire from the clip where the plastic bezel and body meet, then push the wire up between the bezel and body the best you can.
8. Lower the tailgate, open the window and firmly pull the cable up through the space. This may take a few tries if it snags on the hinge or you were not able to get enough wire through the space.
9. Unhook the wire from 2 more clips
10. Take the shorty Phillips Screw Driver, while holding the brake light, unscrew the 2(in our case) screw from either side of the brake light. Some may have a 3rd screw in the center back of the brake light.

2 9" LED Strips from Advance Auto Parts
If you can find an 18” version of this it should work the same. If it is not the same type of light I cannot promise it to fit without more drilling.

3rd Brake Light.
The 2 screws shown here can stay screwed into the housing. You can also see where the 3rd screw might be if it is used on the bezel.

Preview of Mirror Acrylic.
Camera shot of the Mirrored acrylic I am using. I had left overs from a 4x8 sheet I had ordered a while back from Home Depot. You should be able to order/buy this from MOST hardware stores. This acrylic is 1/8” thick which is why I doubled it up. If you don’t want to use acrylic, you could PROBABLY use a thin piece of metal in place of it. Make sure it is really clean before sticking the LED’s to it though. Same for the acrylic but it should be clean if you left the protective sheet on.

Holding down Acrylic for Cutting.
Using clamps at the edge of the table is probably more acceptable but I didn’t have those. I used duct tape to hold the ruler to the acrylic, then once in place, taped that to the table. The big silver square is a computer case side I used to help me hold the ruler from moving (even though it is all taped down).

You can see my scoring marks I did already with the razor blade. Make sure it is a new and clean blade before starting. You will be more prone to cracking or not cutting in a straight line. For your first score of the acrylic, GO SLOW to ensure a straight line. Rushing this part will GUARANTEE it to crack and break. If you veer off your straight line, try coming from the opposite side to correct, you probably only scratched the protective layer (you do still have that on, right?). Once you get a few scores done, you can run it along the straight edge a little faster. DO NOT try to force the razor blade to cut the Acrylic, this will also cause cracking. Try to use an even light to VERY moderate pressure. Once you think you are getting close or hear the first part of it break (good break), use only light runs with the razor blade. Forcing it at this point may cause it to shatter. It took me a good 45min or so and I still cracked it because I got excited at the end. I was able to use it because it did not crack all the way through. The reinforcement will help this too.


Dremel, bit and cutting brake light.
Almost any cutting bit should work for this. I used one that was already in our USED box. Being that this wasn’t a hard surface like wood, I didn’t have a concern for what bit I used. There is minimal force needed to cut out the area of the brake light. Start the dremel in between the red lip and black lip. Grind the red until it is smooth with the facing. You will have to grind out some of the black plastic to get the whole assembly to fit. It should have some form to the shape of the letter “D” but more like |). This will have to be done on the opposite side as well.

Checking Clearance of Acrylic in Light.
Once you have cleared the opening in both sides. Check for clearance to make sure the strip of acrylic will fit. You just need to make sure one will fit at this time. If 1 doesn’t fit, it won’t matter if 2 will or wont. With my piece of acrylic, there were some spots that didn’t break off (seen in blue oval). You can file these off until it is all as even as possible. If it seems like there is still a little too much force needed, take the dremel and grind out the top of it a little more. LESS is MORE in this case. If you make the hole too big, the LED’s may not sit correctly or take more work to get them to sit right.

Acrylic in Light.
Once the holes in the light allow free movement of the acrylic, slide through one side with reinforcement piece (if needed) and LED strip. Do NOT tape or glue anything together yet. You are just making sure the clearance for everything is good at this point.

As you can see in the light, all the plastic shavings. This is where you would take the canned air or air compressor and clean out the light. I used a 20Gal 5HP compressor (obviously overkill but did the job nicely). Once it is free of debris, you are done with that. Do NOT use water!! The LED’s are not made for outdoor use! You can get canned at at almost any local computer store or retail store like Wally World.

Glue used to hold Plexi together.
This was what we already had in the house so I used it. Be careful with these products. The Purple Primer will stain whatever it comes in contact with. We laid a piece of cardboard down (as seen in picture). The glue does not take very long(15-30sec) to start drying.

Apply Glue Primer, Apply Glue next. Do quickly or glue will dry.
When applying primer, wipe off as much as you can on the brush. It does not take much to prime these pieces. Again, caution, it WILL stain anything it comes in contact with! Remove the plastic from the reinforcement pieces if used. I primed both the back of the acrylic bar and the reinforcement pieces. As you can see it “eats” away at the gray backing (pink spots). Do not worry, it does not harm the mirror finish. Put glue down on back of acrylic bar. You do not need huge amounts, just enough to lightly coat the back. Set reinforcement pieces on back, press firmly down for a few seconds. Wait 30sec to 1min before continuing.

See next post.

· Registered
2003 chevy trailblazer_lt_ext
214 Posts
Discussion Starter · #2 ·
Part 2

Please Read!
How do you want the LED’s wired? Series or Parallel?
• Series- Positive of Truck to Positive of LED 1, Negative of LED 1 to Positive of LED 2, Negative of LED 2 to Negative of Truck. The downside to this is if LED 1 fails it will take LED 2 out with it and LED 2 may appear dimmer then LED 1 due to current drop which is used by LED 1.
• Parallel- Positive of Truck to Positive of LED 1 + 2, Negative of Truck to Negative of LED 1 + 2. The plus side to this is if LED 1 or 2 fails it will not take the other LED with it (unless it blows a fuse). The LED’s should also be equal in brightness due to not having the load of LED 1 in front of it.

**It is up to you how you want to wire them. I chose parallel for the benefits of more equal light appearance and redundancy of LED 1 and 2.

The easiest way we found to do this was solder the extra wire to the LED furthest from the right side of the light, drop the LED in from the furthest side through the other side. You should have wire hanging out of the Left side of the Light.

Continue on with removing the protective layer on the acrylic. Peel the red 3M plastic layer off the included double sided tape. Try to center best you can before pressing down to secure location of LED. Do this for the other side as well. Once the tape is in place, do not plan to remove it without having to replace the tape.

Finished without Sealer.
Glue is probably ¾ to all the way settled by now and LED’s have been stuck to the acrylic. Slide the LED bar through the light trying to center the 2 LED strips. The LED’s may not actually be center. When they come on, there will be a slight gap where the 2 LED’s meet. This is what you want to center.

If there is left over acrylic hanging out of the end of the light, you can trim it with a wire cutter. Just clip the edge of the acrylic and it should snap off enough to seal easily. If it is just a fraction sticking out, this should not cause any mounting or sealing issues. You may need to use a little more silicone to make sure it is all the way around the acrylic though. Use your best judgement.

Sealed End.
Used RTV Automotive Gasket Sealer to seal the ends up. You could use almost any type of silicone or sealer. I would not recommend using a hardening sealer just in case you need to remove this down the road.

Other Sealed End.

Light Installed with Flash.
This was the same night as the Light modification was done. We did not drive it that night so it wasn’t an issue mounting and letting set overnight. As long as it is not raining/snowing, it shouldn’t be an issue to mount and drive. Do NOT wash it while this is curing. If you need to drive the truck and it is raining/snowing. Put a piece of tape (electrical, duct tape… etc) or something to plug the hole for the wire. If you do not, it may leak.
Yes, it’s dirty, I know. Lol It was just washed a week ago.


Brakes on with Flash.

Brakes on without Flash.

Just the 3rd Brake light with the sun glare. You can still see it is on.

Whole rear of truck with lights on.

Short Video Clip. Sorry for bumpyness.
3rd Brake Light LED Strip Retrofit

If completed correctly and working, this could save you over $500 (US) from the dealer. 2003 models (and I believe 2002) that have the Neon bulb instead of LED or standard bulbs have to have the Tail Light Assembly replaced along with the Bezel. Plus the Bezel needs to be painted to match your vehicle.

My cost for this project:

Time- about 4.5hrs (with breaks, testing, checking and doing this for the first time)

1.Acrylic- $0 (Already had from previous project, original cost $110 for 4'x8'x1/8" sheet / Home Depot)
2.RTV Gasket Sealer- $0 (Already had)
3.LED Strips- $25 (Advance Auto Parts)
4.Wire- $0 (Already had)

Dealer Cost (My local Dealer in WI):
1. 3rd Brake Light Assembly- $206
2. Bezel for 3rd Brake Light Assembly- $250
3. Paint- $Unkown due to costs above already being too high. This would vary per body shop labor and paint cost.

· Registered
2005 chevy trailblazer_ls
2,037 Posts
:hail:Man that is one heck of a job! You did this yourself and saved a bunch, and by sharing with us you show once again how great this site is! I commend you , you are a true TV contributor!:thumbsup:

· Registered
2003 chevy trailblazer_lt_ext
214 Posts
Discussion Starter · #5 ·
:hail:Man that is one heck of a job! You did this yourself and saved a bunch, and by sharing with us you show once again how great this site is! I commend you , you are a true TV contributor!:thumbsup:
Thank you!

My dad did help some (stupid soldering gun). I can't take all the credit. It was a 95%(me) 5%(dad) but none the less it was a team effort. I know I couldn't find anything detailed on this. I know I wasn't the only one weary about doing it either! :D:woot:

· Registered
2003 chevy trailblazer_lt_ext
214 Posts
Discussion Starter · #8 ·
good write up:thumbsup: well done
Wow, that was excellent. Thank you for the detailed instructions.:D
Thanks guys! Glad it seems to be a useful doc.


The other option would be to get 10mm LED's from Radio Shack. They are a little pricey at 2.79ea and it goes down slightly from there with bulk orders. The plus is they are 28,500mcd which has to be a bunch of times brighter then this option. I chose this for cost savings but maybe will switch later on.

· Registered
2003 chevy trailblazer_lt_ext
214 Posts
Discussion Starter · #9 · (Edited)
In case anybody wanted/needs them.

Some more pics.

Location of 3rd screw.

Overview and locations of all 3 screws.

Wire clip. After pulling down weatherstripping by rear dome light, this need to be pried up with a small screw driver then pulled out.

Wire hold down between tailgate and bezel.

Location of three wire hold downs. Make sure they are pressed in good or you may risk pinching them in the hinges.

· Registered
2002 gmc envoy_slt
4 Posts
Before I start cuttin', will the Avalanche light work??

I have a 2002 GMC Envoy SLT. I've seen the posts where the Trailblazer folk are able to retro fit an avalanche light into their trucks with a minimal wiring change. My question is, will the avalanche light fit the 2002 Envoy, or are we stuck doing our own mod? Thanks!

· Registered
2005 gmc envoy_sle
244 Posts
I have a 2002 GMC Envoy SLT. I've seen the posts where the Trailblazer folk are able to retro fit an avalanche light into their trucks with a minimal wiring change. My question is, will the avalanche light fit the 2002 Envoy, or are we stuck doing our own mod? Thanks!
If the lights on the 02-09 fit the same, the Avalanche should fit. I think going with the Avalanche would save me 4.5hrs and cost me about $60. But damn! that light looks good.

· Registered
2003 chevy trailblazer_lt_ext
214 Posts
Discussion Starter · #13 ·

2yr update. (Wow its been that long already!)

A couple of the leds stopped working and some of the double sided tape started to let go. It hasn't prevented it from working completely and the tape hasn't changed visibility. I am probably going to look at the lights mentioned above or see if I can do a better job on this one.

Thanks again,

· Registered
2003 gmc envoy_slt_xl
1 Posts
So awhile back my wife was driving to work and was running late as usual. she heard a whack on the back window and pulled over the third brake light assembly had broke loose and was hanging only by the wires. She decides that she is late and continues to drive until it broke the wires and fell on the highway leaving it there. :duh: Parts were quoted to me at 500+ :sadcry: So we went with out for awhile until went to have it inspected for new tags. It won't pass.
So I made an assembly using aluminum diamond plating and a trailer LED light bar and paint for under a hundred I made a new third brake light assembly and if some one tells me how to post pics on here I will glad to show it off.
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