Hi all,
I can't be the first person to install an LED tail light bar on the 2021 truck. I need help. I have an XL with the basic bulbs. I need to hard wire the LED bar in to the truck because....well first because it's stupid to just plug in the four way connector, and second I will get all sorts of error messages every time I start the truck etc etc. But how do I wire it in to the tail light when there are separate wires for turn and brake but the light bar just has one wire for left turn/brake, and right turn/brake? What did you all do? Any help would be appreciated.

 

A few videos on Youtube addressing the topic...they might give you some ideas...

 

Dude, I have watched at least ten of those videos. None of them deal with a 2021, and none of them deal with the issues when you just plug it in to the 4 way trailer connector, and none of them address the issue of how to hard wire when you have a separate wire for tail light and brake like these 2021 do. One of those projects that should have been so easy, but .... And with not so many 2021's on the road, I don't get as many responses as when I was in the OBD forum.

I know I should just cut off the 4 way plug and experiment with the wiring to see what works but I am a cheapskate so if it doesn't work, I'd rather return it and move on. Just hoping someone else figured this out already, or knows enough how to help me. A rear tail light bar seems like a common project. I can't believe nobody else with an XL and bulbs hasn't figured this out.

 

Anybody familiar with Zener diodes? Sounds like I could use them to attach the tail and brake both to the standard four pin trailer wiring of the LED tail light bar. I could use some help with coming up with a diagram though as I have never used them. Thanks.

 

I think I understand your problem a little. If I understand correctly you are trying to run led light strip through the trailer wiring. Problem with that is led strips don't draw enough current for the truck system to recognize it. I had a similar problem adding led lights to boat compartments that had standard bulbs. The solution for the boat was to put one standard bulb in the circuit so the computer could see it.

I am pretty sure there are kits out there for this purpose but before you do purchase one try to put a standard bulb in the circuit and see if the led's work before spending any more money. Don't put the bulb in series, put it in parallel with the light strip wiring. You need just enough current draw for the computer to see the light strip. Hope this helps.

Edit to add: Upon further thinking (and I've never tried this) you might be able to read the resistance across a 1157 stop light element and purchase a resistor in that same range. Again, wire it parallel with the led strip wiring and that should resolve your issue. Purchase a 5 watt resistor and put it where it can cool down if needed.

 

No, I am not trying to run it through the trailer wiring, as that causes all sorts of known error messages. I am trying to hard wire it in to the actual tail lights. I have an XL with halogen bulbs. But most if not all LED tail light bars are wired for a standard 4 pin connector. Well this 2021 F150 has a turn bulb and a separate brake bulb which doesn't match a trailer four pin connection. So how does one get around this issue. Someone suggested I use a diode to be able to wire it up, but other than the suggestion there was no more info. Just trying to do a simple mod. Trying to learn more. Thanks though.

 

OK, now I understand. You need something like these. These will adapt a standard bulb trailer to a multi bulb truck like yours. You only need two as this kit also is for tail lights. Demco Diode Kit | eBay

 

Hmm, interesting. I will take a look and report back on my progress. Thank you for the advice.

 

I have a motorhome that has red stop lights and amber turn lights. I tow the wifes Cadillac SRX which is red/red for turn and stop. I had to install these to make it work with those standard lights. They will work for what you want to do. FWIW, You should be able to purchase a adapter kit from Hoppes or one of those trailer wiring companies that would plug between the connectors at the back of your truck. This would save you all the headache of tapping into wires and possibly creating other issues. Plug the Hoppes between truck harness and trailer receptacle and use those wires to your light strip.

 

I have a 2020 STX that I installed one of those light bars on the back (and love it). I also didn't want the error codes and I wanted the backup light to work as well. The one I got said to tie it into the wiring harness of the truck but I didn't want to do that. If I screwed something up I didn't want to have to pay to have a wiring harness repaired/replaced. I ended up googling the wiring diagram of the tail light assembly to get the color codes of the wires I needed to splice into. It was a bit more work and I had to take the whole tail light out of the truck but that wasn't as bad as it sounds. You can unplug the whole thing from the truck's main harness to make it easier to splice the light bar wiring into it. I did it this way figuring that if I screwed something up, worst case would be that I spend a couple hundred bucks on a tail light assembly. It doesn't matter which tail light you use to pick up brakes, lights, and reverse, but you do have to run a wire from the other side to pick up the other directional. I have a 2022 on order and I won't hesitate to do the same thing again. I live in upstate NY with harsh winters and this install has gotten through two winters without a hitch. The splices are also better protected tucked up into the tail light assembly.

 

My 2022 arrived much earlier than expected and I installed a new light bar onto that. What I didn't realize until I installed the light bar is that Ford changed to amber turn signal bulbs and I had to splice a second brake wire into the light bar. It still worked out just fine and everything works great. It should be noted that my truck is an STX so it has the standard bulbs in the tail light and the light bar is LED. I hope this helps.

 

So Saragnac....how and where did you hook up your wires? And you lost me on the second brake light wire...

 

I took the whole tail light assembly out of my truck. It's not hard to do, two screws (I used a nut driver) and the whole assembly comes out. You can then unhook the wiring harness and completely remove it from the truck. I did this and used the bed of the truck as my work. My light bar kit came with about 5 feet of 4 wire trailer harness with the male end so I ran that wire from underneath up through the hole where the tail light goes and back onto work area. I couldn't find an online wiring guide but it really wasn't hard to figure out which went to what and I simply used those splicing clips to splice into the tail light assembly. I did look up the standard 4 wire code so I knew which went to the left and right signals. I did most of the splicing on the drivers side tail light but for the right signal light, I peeled back that wire from the 4 pin harness included in the light bar kit and ran it to the right tail light. When I tested this the first time, everything was working except the brake light would only come on as the normal tail light brightness, it wouldn't get very bright. I noticed that there were two brake/tail light bulbs in the assembly so I took the second tail light wire (which was a different color than the other) and spliced it in with the first. Now everything works perfect. Once you wire up the left tail light, the 4 wire trailer light kit will drop down underneath the truck below the left side. This is where you take the single, right signal wire you peeled off the 4 wire kit and bring it to the right tail light to splice it in. This side goes quick since it's just one wire. Once you have that spliced in, tuck and zip tie all the wires out of sight, plug it into the trailer light adapter that is attached to the light bar. Also, I removed the tailgate for this job. All total this took my about an hour and a half to do.

 

A big thanks to Saragnac for the help. I got bored over the Thanksgiving break and finally dove in to this project. I did as suggested and tapped in to the tail lights. Wasn't too hard, but I don't have much experience with electrical stuff so I went slow and laid off the beer until I was done. I had to add a wire to the tail light wire to connect to the brake wire in the tail light assembly but all the functions work. When i first tried everything the left turn signal kinda stuck on for a few seconds. But it went away and has worked normal since. My truck is oxford white so I like that the light bar fills in the gap under the tailgate. I really like the added light for the morning commute, plus the cool factor.

 

Not sure if this is your prob. But I am going to mount a high mount brake light on canopy I built. There is a loose wire in the engine bay, on the side. It's for that very purpose. It will trigger brake light, but not flash turn signal. Just got to run it to rear of truck.
lol, that's what the internet says! Haven't gotten to it yet!