Camper top 3rd brake light

[Shrek The Raptor]

I’ve searched high and low… I can’t find an answer

I have an Ali Cab on the truck, and the prior owner didn’t wire up the 3rd brake light. No biggie, run wires to the trailer harness. Can’t do that, the truck thinks there a trailer. Fine, run it to the brake light harness. Found the correct brake wire, but now, since the brake light receives power with the running lights, the 3rd brake light is also dimly lit with the running lights on. I don’t have it, but if anyone has a working solution, would love to hear it.

Sponsored

 

[SurfRanger]

I did a ton of debugging on this and created my own custom solution for a custom third brake light.

What i can tell you is that the brake light wire carries two signals: ~6 volts for running light and 12v when brake is applied. Thats why its dimly lit when running. If you dont want this behavior, and only want the brake to light it up. Just put a normal 12v relay in between the harness tap and the 3rd brake light. It will not engage at 6v and will engage at 12v.

lemme know if u have any other questions.

 

[Shrek The Raptor]

I did a ton of debugging on this and created my own custom solution for a custom third brake light.

What i can tell you is that the brake light wire carries two signals: ~6 volts for running light and 12v when brake is applied. Thats why its dimly lit when running. If you dont want this behavior, and only want the brake to light it up. Just put a normal 12v relay in between the harness tap and the 3rd brake light. It will not engage at 6v and will engage at 12v.

lemme know if u have any other questions.

Ahhh that makes a lot of sense, I sorta assumed with how many wires there were, that maybe it was lighting up an additional section of that upper portion, but 6/12v makes sense.

Thanks for the tip!

 

[SurfRanger]

Yea i made this for my camper. White runs off reverse trigger from tail light, 6v triggers the low power light of the red lights for running, brake light powers the high power mode of the red lights, and then an aux switch powers the ambers.

 

[ShadowDragon24]

As per the Ford Body Builder Layout(aka upfitter guide) you tap the 3rd brake light at the bcm. I put an led in my 3rd brake, then I ran a 3/1 core with 3 14g wires in it under the truck following the factory harness, and in the same plastic channel they have(that was a bitch to do) for the ground for my cap. the bcm brake is then tapped, ran out through the firewall, hooked into the wire I just ran for the brake for the C1R's(gets rid of the trailer disconnected error as I took the brake/turn singal wires off the Diode Dynamics harness, except for the ground, marker, and reverse wires) and brake for the cap , and then fused power off the low draw side of battery to the 3rd wire, ran back for dome lights in the cap.

also under the bcm per the upfitter guide there are 3 blunt cut wires, a marker light trigger, a high beam trigger, and a ignition trigger. I have these hooked into my diode dynamics dswitch to automatically turn on and off(can still use while truck off) will automatically turn my dswitch night mode on, and my grill lights) and the highbeam will turn on when ever I got programmed into my dswitch. right now it turns on my lightbar

 

[SurfRanger]

Looks like a clean and good install!

i have power in my bed from a house battery so i actually use that to power these and the just use the lines coming of the the brake light harness as trigger wires so they arent really pulling any power.
I also used a 3rd party piggy back harness that has the oem tailight plugs kn them and just slots between the oem wire harness and tail light so I’m not stabbing any wires.

 

[ShadowDragon24]

Looks like a clean and good install!

i have power in my bed from a house battery so i actually use that to power these and the just use the lines coming of the the brake light harness as trigger wires so they arent really pulling any power.
I also used a 3rd party piggy back harness that has the oem tailight plugs kn them and just slots between the oem wire harness and tail light so I’m not stabbing any wires.

I also have an aux battery. using the ARB dual battery kit, that comes with a charger. thats my D-Switch is mounted on.

 

[SurfRanger]

Nice! Mine just happens to be in the bed so its near the brake light obviously.

Also ps thats the most full windshield washer reservoir ive ever seen hahaha

 

[SLJ]

That's way too much work.
Mine had a little module maybe an inch by a half inch and a quarter inch thick that took the brake light signal tapped from both brake lights on the rear. That way the only time it came on was when both brake lights were on so a turn signal didn't trigger it. Truck doesn't see it so it doesn't mess up anything. A truck cap brake light module is about $20.

 

[SurfRanger]

That's way too much work.
Mine had a little module maybe an inch by a half inch and a quarter inch thick that took the brake light signal tapped from both brake lights on the rear. That way the only time it came on was when both brake lights were on so a turn signal didn't trigger it. Truck doesn't see it so it doesn't mess up anything. A truck cap brake light module is about $20.

Yup ive seen those as well. Glad it worked out!
I didnt want to run wires to both brake lights. I also went way overboard because of my setup but i had the standard brake light before and just did the normal brake light tap. Yes it showed dim for running lights which i think is fine actually. Then brakes made it go bright. No modules involved.

 

[alpaca-harebell]

What i can tell you is that the brake light wire carries two signals: ~6 volts for running light and 12v when brake is applied. Thats why its dimly lit when running. If you dont want this behavior, and only want the brake to light it up. Just put a normal 12v relay in between the harness tap and the 3rd brake light.

Great insights! What did you use for your clean 12v power source in this setup?

 

[SurfRanger]

Great insights! What did you use for your clean 12v power source in this setup?

I have a house battery in the bed that i ran power from for clean 12v so i wasnt pulling power from the taillight. Could also be done by just plugging into the cig plug in the bed i suppose. I think that ones live anytime the car is on but i could be wrong

 

[millsner]

does anyone who tapped directly into the rear brake lights have photos or a diagram so I know which wires to tap into? I can’t seem to find any information.

im sure this is what everyone’s looks like?

Clearly, I'm pretty inept with these things…

 

[ShadowDragon24]

both left and right side wiring for my 2025 xlt with the level 2 tails(not full led like raptor)

Sponsored