Rooftop Tents blocking brake lights (CHMSL)

[jjswan33]

@avigneault - one additional quirk I am seeing with always on power. I see that the brake light randomly turns on sometimes and then doesn't go off.

My theory, the truck senses a key nearby and does that weird thing where the lights quickly flash and that triggers the 3rd brake light, due to how fast the flash is it doesn't get the off signal fast enough and stays on.

Not really a big deal because it is only pulling 5W and it isn't on my truck battery. Also easily solved by hitting the brake or cutting the power. Bottom line I may consider using a switched vehicle power source at some point.

Sponsored

 

[avigneault]

@avigneault - one additional quirk I am seeing with always on power. I see that the brake light randomly turns on sometimes and then doesn't go off.

My theory, the truck senses a key nearby and does that weird thing where the lights quickly flash and that triggers the 3rd brake light, due to how fast the flash is it doesn't get the off signal fast enough and stays on.

Not really a big deal because it is only pulling 5W and it isn't on my truck battery. Also easily solved by hitting the brake or cutting the power. Bottom line I may consider using a switched vehicle power source at some point.

Good call out. The 12v gear tunnel outlet is switched.

 

[Soju1]

Could one tap into the 12v jumper leads that’s on the right side of the hitch. It’s it’s used to jump start the 12v battery, I would think you could draw power from there too

 

[Riviot]

Dumb question, a quick DuckDuckGo didn't answer it:

Are there OBD-II connected wireless brake lights? Plug-in or battery powered, but the braking on/off comes from the plug?

No one answered my dumb question

I ended up forgetting where this thread was and wiring up a trailer plug light to my bike rack. I'll test functionality and driving impacts Friday.

 

[HighVoltOverland]

Arise my zombie thread!

does anyone remember off the top of their head if the tailgate light bar functions as a break light or is it just always on / ambience?

getting my gfc installed next week and rumor has it they couldn’t figure out brake light wiring

 

[jjswan33]

Arise my zombie thread!

does anyone remember off the top of their head if the tailgate light bar functions as a break light or is it just always on / ambience?

getting my gfc installed next week and rumor has it they couldn’t figure out brake light wiring

pretty sure always on/ambience. Not surprised they couldn't figure out brake lights, it's incredibly complicated. There is no way to just tap into the brake light, it's just a power, ground and signal.

Too bad Rivian hasn't come forward with a solution like they said they would.

It would be trivial to allow us to plug into the hitch wiring without nerfing the truck or the long promised brake light accessory.

good luck.

 

[HighVoltOverland]

pretty sure always on/ambience. Not surprised they couldn't figure out brake lights, it's incredibly complicated. There is no way to just tap into the brake light, it's just a power, ground and signal.

Too bad Rivian hasn't come forward with a solution like they said they would.

It would be trivial to allow us to plug into the hitch wiring without nerfing the truck or the long promised brake light accessory.

good luck.

Would the solution not be to just use a regular 2to3 harness?
Plenty of other non Rivian trucks that have the BCM control the brake lights

 

[HighVoltOverland]

Spoke to my buddy today who works at Rivian
He showed me where the wire to the chmsl is in the rear passenger pillar
He mentioned that the service trucks use this same location for their auxiliary light

I’ll share pictures later in the week when I wire mine up

 

[SJaYx2P]

Looking at the existing CHMSL light strip there seems to be one harness towards the left end.

Looking at a picture of the roof spoiler guts, I believe the wires connected to it are solid green and black.

In the pillar beside the rear driver side door there is only one set of wires running up to the roof. Within the set is the same solid green and black wire.

Does anyone want to see if tapping these wires would work. I don’t have any taps at the moment and I’m too chicken poop to cut them.

 

[HighVoltOverland]

Wiring the rear brake light:

Step one
Remove the rear seat bench
it is held in with two 15mm bolts under the headrests, on bolt on the bottom middle (15mm ) and one nut centered under each passenger back area (15mm as well)

don’t forget to unplug the two white plugs behind the seats.
Once removed, pull the small kick/ sill plate from the driver side floor

peel up the next two trim pieces, the dark grey going up the side and the lower headliner piece that matches your interior and has the seat belt passing through

In the loom locate the plain green and plain black wire (black wire is smaller 22awg)

verify it is the plain green and not the stopped green

this is the chsml pair

I tapped into the wires using a positap
Highly recommend
You can get them at O’Reilly or Amazon

In the truck bed remove the rear plastic panel it is held in with 8 M6 (10mm socket) bolts that are hidden under the plastic circles

once pulled you can see the tonneau stack if you have it and a few grommets

I don’t have a tonneau so I used the higher location to not have to fiddle with the sliding over the gear tunnel

you can use the lower grommet and fish any wire around the felt of the gear tunnel and out the space behind the passenger seat

Drill a hole in the plastic piece in the location of you liking, or figure out a seam to tuck the wires through if you are nervous about drilling

I don’t like pinching wires so I went the hole drilling route and will use a weatherproof mini box as I have other cables using this area to run power

hook up the lights to the provided pigtail (gfc came with some positaps, which I moved to the splice location, and then used the twist connectors to connect the short length of jump wire needed

that’s it!
It works

No extra sensors or modules to burn out
No false trigger of trailer mode
No issues with turn signal behavior

it just works.

 

[AltaTruck]

I just got done wiring my rear lights the way (sort of) you described. The very first bolt I tried to remove snapped the retainer for the nut and there was no way to get it or the seat out. I was able to remove the pieces of trim and attach the positaps to the wires in the harness. From there I routed it under the trim and followed the existing harness. I went through the upper grommet in the bed and under the left bed wall. It works perfectly and looks like factory. Thanks for the heads up on where to hook up to the truck's system. Putting the motorcycle across the back on a hitchhauler blocks the lights pretty effectively so this was a must.

 

[guydesharnais]

Wiring the rear brake light:

Step one
Remove the rear seat bench
it is held in with two 15mm bolts under the headrests, on bolt on the bottom middle (15mm ) and one nut centered under each passenger back area (15mm as well)

don’t forget to unplug the two white plugs behind the seats.
Once removed, pull the small kick/ sill plate from the driver side floor

peel up the next two trim pieces, the dark grey going up the side and the lower headliner piece that matches your interior and has the seat belt passing through

In the loom locate the plain green and plain black wire (black wire is smaller 22awg)

verify it is the plain green and not the stopped green

this is the chsml pair

I tapped into the wires using a positap
Highly recommend
You can get them at O’Reilly or Amazon

In the truck bed remove the rear plastic panel it is held in with 8 M6 (10mm socket) bolts that are hidden under the plastic circles

once pulled you can see the tonneau stack if you have it and a few grommets

I don’t have a tonneau so I used the higher location to not have to fiddle with the sliding over the gear tunnel

you can use the lower grommet and fish any wire around the felt of the gear tunnel and out the space behind the passenger seat

Drill a hole in the plastic piece in the location of you liking, or figure out a seam to tuck the wires through if you are nervous about drilling

I don’t like pinching wires so I went the hole drilling route and will use a weatherproof mini box as I have other cables using this area to run power

hook up the lights to the provided pigtail (gfc came with some positaps, which I moved to the splice location, and then used the twist connectors to connect the short length of jump wire needed

that’s it!
It works

No extra sensors or modules to burn out
No false trigger of trailer mode
No issues with turn signal behavior

it just works.

I followed your instructions and YES it does just work! Thanks for your great documentation, MUCH appreciated.

 

[tako]

Arise my zombie thread!

does anyone remember off the top of their head if the tailgate light bar functions as a break light or is it just always on / ambience?

getting my gfc installed next week and rumor has it they couldn’t figure out brake light wiring

I have a gen2 R1T with a GFC and the installer did not wire in the brake light. I still haven't got mine working yet, but the light bar is just a running light. The brake lights are small and in the rear corner tail light assemblies. I was able to test the GFC light by using a trailer hitch adapter for active high Brake signal and GND, however this solution triggers trailer mode which limits emergency breaking and disables ACC, so I didn't fish the wire through as I didn't like this solution.

Next test will be to tap the back side of the trailer hitch wire, to see if the hitch plug is what is triggering the trailer mode, or if it is an electrical load on the brake line. I'm also concerned that the brake signal will not activate on this assembly if a trailer hitch plug is not detected.


This triler hitch plug was helpfull in diagnosis, as you can re-wire each signal and run your own wire.


I would love it if Rivian introduced a feature to enable the RGB LEDs under the light bar (used to indicate charge level) as an alternative CHMSL, or used the center light bar running light as a brake light.

 

[GreenLightning]

This is a fantastic idea. Yes @Wassym is there any opportunity to have the center light bar use a middle section to emulate a third brake light? Lots of us out there with the rooftop tents that are now missing our third brake lights. This would be a GREAT solution to the problem

 

[Tucker74]

Thanks @SJaYx2P - finally got around to doing this today and worked great. I was able to just remove the rear panel and fish it through the upper unused grommet. Didn’t have to remove seat, just pried back trim and spliced with the positaps

Sponsored