Meso Customs BD4 Third Brake Light Install - A Layman's Guide

Hey TW,

Over the weekend I tackled the install of my third brake light, housing from Meso Customs, and four rock lights from Baja Designs (courtesy of Hotshot Offroad). We had some gnarly storms here since that install, and thankfully I installed it correctly enough to report back that there were no leaks despite the massive downpours we experienced. That being the case, I thought a write-up might help those of us in the future who have no experience in electrical installs like this. I have no previous experience with any of this, and even I managed to finish my install with no issues aside from dropping a few clips, so I'm confident that if I can do it, you can too!

Please note: This will only apply I believe to Double Cab 2016+ Tacomas. Some instructions may apply to other models, but I can only say that this 100% works for 2016+ Double Cabs. Also, Baja Designs' official stance is to use a relay for this setup. I don't know what that means, so I did not do that lol. I am not experiencing any issues at the moment, but I am aware that that does present issues if I need to file a warranty claim on the lights. I know it's a risk, but I had no idea how to proceed there.

First things first, let's break down what I used:

• Meso Customs BD4 third brake light housing
• Baja Designs Rock Lights
  • Two Red Lights for the Brake
  • Two White Lights for the Cargo
• 200pcs Heat Shrink Butt Connectors Terminals, Eventronic Insulated Waterproof Marine Automotive Copper Wire Electrical Kits (3 Colors 3 Sizes)
  Butt Connectors (this link includes an extra size, but it's a fair price)
  
  • 18-22 AWG
  • 14-16 AWG
• $18 Southwire Right Angle GFCI, 2Ft Right Angle GFCI Extension Cord, Tri-Source, Yellow, 14880023-6
  Wire strippers
• $26 Southwire TCC9D 9" Terminal Crimper/Cutter with Dipped Handles
  Crimper
• Primary Wire (up to you if you'd like to only use one color or multiple. I used black, red, and white to differentiate what wires led to what. The wire I bought at Lowes only came in one size, 16-19 AWG, so I'd recommend that since it worked!)
• Heatshrink (Probably useful to buy a set of different sizes, but your move)
• Heatgun (for heatshrink, but a hair dryer would probably work too if you don't care to buy one)
• $11 Michigan Motorsports Weather Pack 2 PIN Connectors 5 Sets 12-16 AWG used for cars, trucks, motorcycle, boat, trailer, marine, jetski (2 PIN)
  Weatherpack Connector (This link will include more than you need, but useful to have multiple because I fucked up a few pieces through trial and error. I also used a 3-pin connector but that was my mistake, a 2-pin connector would work too.)
• RTV/Silicone (I recommend clear or black, but your choice)
• Plastic Razorblades

Now let's get to the fun part. There are going to be a couple of photos and videos in this post, but I will say that I didn't do the best in terms of taking photos along the way. I'll do my best to be really thorough in my text to make up for that!

1. Take your BD4 brake light enclosure. You can see that there two sets of holes in each recess where your rock lights will sit, but it's important to note that these holes aren't threaded yet. They're self-tapping, per Meso's comments here, but you need to run the hex screws that will hold your lights in place into the holes first so that you thread it. No need to go all the way in, but put some pressure behind the screw and drill it in so it'll grip when you install the lights.
   • There are four spots for your light, but notice how two are angled down on the ends, and two angled straight ahead in the middle. The white lights should be angled down to light your bed up, and the reds should be mounted straight so that your brake lights are easily seen.
2. Take your red rock lights, wire the wires through the small port in the bottom of the middle recesses, and push the two red lights all the way into the housing. You can screw the brake lights in so that they're completely mounted. You don't want to do this yet for your white lights, as you'll need to access the screws behind them to secure the housing to your truck.
3. Wire the white lights through their respective ports the same as the previous step, but as I said do not secure them yet. Get them as close as possible to give yourself as much slack in the wire, but don't secure them yet.
4. Wiring: This part can be really intimidating, but just take your time and you should be fine. I'm going to include diagrams that should help.
   
   • Each Rock light comes with two wires: a positive and a negative. The black wires are your negatives, and your red wires are your positives. These wires will most likely come wrapped in a heatshrink casing that keeps them together. You can trim this casing so that you have more slack to work with for the individual wires within it but be careful to only cut the heatshrink and not the wires themselves.
     
   • We want to combine the negative wires (4 in total) into one wire.
   • We want to combine the positive wires of the brake lights (2 in total) into one wire.
   • We want to combine the positive wires of the cargo lights (2 in total) into one wire.
5. See the diagram for a simple representation of what we want the final product to look like.
   • Expanding on the diagram above, you'll combine all 4 negative wires from the rock lights into one single 14-16 AWG butt connector, and then splice some primary wire into the other side of the connector. This wire will be your ground (we don't want to use the factory ground wire from the connector, not enough power will get to your lights.) Make sure you keep this ground primary wire extra long for now! We're going to run this through the headliner later, so don't shoot yourself in the foot by cutting it right now.
   • Combine the two positive wires from the red rock lights, put them in an 18-22 AWG butt connector, and splice in the primary wire into the other side of the connector. If you're using the three different colors of wire as I did, you'd use the red wire here. This wire can be shorter than the ground. I'd say 6-8 inches is more than enough for what we want to do.
   • Repeat the previous step for the remaining positive wires from the cargo lights. You can use the white primary wire here!
6. Now that you've got your little wires from the rock lights connected to the primary wire, let's add some heat shrink around those connectors. This will serve to waterproof the connection and keep it secure. I would add heatshrink to any portion of your setup that those small wires are visible. They're pretty thin, so the last thing we want is them getting damaged.
   
7. Now we're going to take the ends of our red and white wires, strip away a little of the casing so we've got about 1/8th of an inch of exposed wire, and connect these to our weatherpack pins! For sake of this tutorial, we want to connect these wires to the male pins of the connector. This video is a good tutorial if you've never done this before. Once the pins are assembled, put them into the plastic connector casing, keeping note of which letter your respective wires are placed in. (A is Cargo, B is Brake, etc.)
8. On the other side of this weatherpack connector, the female ports, we're going to use the connector that Meso Customs ships with the housings. See the below diagram that Meso ships with the housing. I'm referring to the little box with the Meso logo on it.
   
   • If you're looking at the connector from the front, the brake light should be the left wire, and the cargo should be the right. This was true for me, I'm assuming it's true for you as well!
9. Now your weatherpack connector should have your BD4 with all of its wires leading to your ground wire, and your weatherpack connector's male portion, and that will finally plug into the female portion of the connector, that is now connected to your Meso Factory Harness Connector! Congratulations, the hard part is done! You're all set for install! Not the best picture, but here's what mine looks like at this stage!

~~Prep Work~~​

At this stage of the install, we want to do some little preventative measures to make sure our install goes smoothly and we don't experience any leaks in the headliner. This is where the RTV comes in.

1. Take your RTV/Silicone, and we're going to do a nice bead of it around the entire perimeter of the BD4 casing. There's a weather seal that Meso has incorporated into the casing already, and it should get the job done, but it never hurts to be paranoid about this! You can see this weather seal in my previous photo. Just put a good amount of silicone around that perimeter, and let it sit for at least an hour so that it dries. Your plastic razorblade will come in handy here if you care about it getting on the sides of the housing. I did.
2. You're also going to want to seal the holes where your rock light wires are coming out with silicone in order to ensure no water leaks through there. BUT WAIT: make sure you're only sealing the brake lights' holes right now. You don't want to seal the cargo lights' holes as they're not in position, you'll end up fucking yourself over and preventing the cargo rock lights from sitting flush in the housing. I'll let you know when to apply that silicone.
3. IMPORTANT STEP HERE: DISCONNECT YOUR BATTERY. DO NOT GO FORWARD WITHOUT DISCONNECTING YOUR BATTERY.
4. Here's where you'll need to make your own decision: Do you want to keep your OEM third brakelight in case you want to go back to stock? If so, you'll want to remove the brakelight from the interior, which means dropping the headliner. I did not do this method, so I can't really assist much, but others have done so in this forum so you'll find guides if you search! This is a good one to start on. However, if you don't care about your stock brakelight, then I can help. You can just drill out the studs that are holding the brakelight in place from the outside, but this will effectively kill the OEM brakelight. Ronzio goes into detail about how to do so here on this thread. I went with this method, and don't regret it. Once you get the original brakelight out, we're almost ready for the install.
   
5. You're going to need access to a ground bolt in the install, so it's best to get that ready now. In your back seat, fold your seats all the way down (pull the little nylon handles to release them and lean them towards the front seat).
6. On the Driver's Side back seat, you want to pop the C pillar(?) off in order to access the ground bolt. In order to do this, you'll need to pop open the little Airbag symbol (don't worry, it shouldn't go off here. Just be gentle.). See below image.
7. Behind this, there's a bolt. Use your socket wrench to release this bolt, but make sure you don't drop it! It's going to make your entire day miserable if you drop that bolt, so make sure you don't lol. I believe this is a 10mm bolt but can't say for sure. Once this bolt is out, you can pop the panel forward. Be careful as you pull it forward, as there are clips keeping it secure throughout. It doesn't have to come off completely, but you need room to get your hand and a socket wrench behind it for the ground bolt later.
8. Lastly, for the prep work, you'll need to give yourself some slack in the headliner to get our ground wire to the bolt. The clip in the image below is what's keeping the headliner from dropping at all in this area, so just pop this out and it should give you enough slack. Don't be rough with the headliner, though! It can crease if you really bend it, which is going to look shitty.

~~Install~~​

We're ready to get this thing on the truck! Hop up into your bed, and let's get it.

1. First things first, we need to test the wiring. The moment of truth. Plug your Factory harness directly into the Meso Harness connector, and it's that easy! get your ground wire, and throw it into the hole for the brakelight, and snake it as far as you can to your left towards the driver's side. Hop down out of the bed and go over to your driver's side rear door and locate your ground wire. It's most likely going to be visible where you gave the headliner slack. Pull that through and route it so that it's behind the C Pillar. This is where you can trim your Ground wire to the length it needs to be to reach that bolt.
   • Once the ground is trimmed, the last thing to do to the wire is strip the casing, and splice it into the mounting clip that Meso includes. This looks like a butt connector but has a flat metal ring on the other side that will go around the ground bolt. Use your crimper to do that.
   • The ground bolt we're going to attach the ground to is easy to find. It's a little below eye level, and it's currently holding a wire underneath it. I really wish I had a picture for this, but hindsight is 2020. Regardless, it's the only main bolt that is in this area, so it should be easy to find. Unscrew this bolt, making sure not to drop it, and add the ground connector to the bolt and remount. The ground is connected now!
2. Reattach your battery, wait 10 minutes, and start up your Taco. Make sure your cargo and brake lights are working properly, and take a big victory swig of your alcohol of choice to celebrate your achievement! It's smooth sailing from here. Before moving on, disconnect your battery again!
   
3. Your BD4 is most likely going to come with these jack nuts attached to the mounting bolts. All you want to do is unscrew them from the bolts in your BD4, slide them over the holes where the original brakelight was mounted, and this will serve to act as the threads that your mounting bolts will screw into.
4. Make sure all of your wires are safely inside the opening for the brakelight, and if they are, go ahead and mount the brakelight to the jacknuts. Don't go insane on tightening them, as we don't want to break the housing, but make sure it's flush and you can't pull it away from the body at all.
5. This step requires some speed. You're going to need to apply some silicone to the wiring holes for the cargo lights, and then quickly push the lights into their recesses so that they sit flush. Be careful here, as you don't want to damage the wires. I did little practice movements before attempting, which was useful as the wire of one did get caught up until I rotated it a bit. Once you're confident you can do it, apply the silicone and push the lights flush. Screw them into place, and then you're done mounting!
6. This last step is optional, but I did apply a light bead of silicone onto the top of the area where my truck meets the new BD4 housing, just in case. Up to you.
7. Finally, put your C Pillar and headliner back into place, and marvel at your new badass brakelight setup!

Please feel to ask any questions, I will do my best to answer any that anyone has! I really think that this install is manageable as long as you take your time and make the proper preparations and do your research. Hopefully, this write-up helps you!

See below for my final images!

 

Nice guide!

Any reason you went with a connector between your lights and the @MESO connector? Now it goes Lights > Connector > Connector. I think it’d be more streamlined to go Lights > Splice (you choose) > Connector. I made one up for @CherokeeCajun this way and it makes it pretty simple. Still need to put the ring terminal on for ground


For wire, primary (hookup) wire is okay, but I think the OE match is XL series. It’s a little more heat resistant. Otherwise, this will be super useful for people! Thanks for sharing.

 

Ahhh I see what you're saying! I had accumulated a bunch of mismatched guides on others' installs, and only really understood the use of the butt connectors. I think your method is probably the easier way, and definitely less bulky! I ended up going with what I used just because it was the only thing I really understood and was honestly a little worried about messing up the wires that the lights came with! Felt the butt connectors and weatherpacks allowed me to mess up a few times without any massive damage. But seeing how minimal your setup is, I think I would definitely choose that if I needed to do it all over!

I realize now that I made it harder on myself by adding in the weatherpack connector when I could’ve just as easily used some more butt connectors where that is now, or even further up the setup. I kind of hobbled together my wiring from different videos and posts here, but hey, you live and learn!

 

Nice write up

 

Just got my MESO 3rd brake light, going to tackle this soon. Now I'm off to the bank tomorrow to get a loan to buy the Baja lights.