Topper 3rd Brake Light Wiring Harness

[MTMan]

Is there a way to make adding a topper for the 3rd brake light plug and play? Anyone have part numbers for connectors?

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[Big Dog Daddy]

Paging @powerboatr
This one's for you Sir.

 

[powerboatr]

Is there a way to make adding a topper for the 3rd brake light plug and play? Anyone have part numbers for connectors?

Wire is under hood near air box filter thing .
It's buried in a wire harness
If you have a pb. Tye circuit has to be enabled in forscan
Also the wire only works. No matter if a pb or non pb. If key is ON
It does not work as the brakel8ghts do if truck is off
You will need to run a protected wire to rear of truck and up to toppers brake light wire
I ran mine through the frame
Similar to how I ran wire to aux rear lights

 

[MTMan]

Oh wow. I was originally wondering about getting a taillight harness male/female plugs with terminals for plug and play as opposed to the 3M taps SmartCap uses since they integrate turn signals however I prefer just brake. Is it a legal thing?

 

[powerboatr]

Some places tap the drivers side rear tail light harness...that's the easy way..
The uppfitter book states to use the provided wire under hood

I guess if scotch look or tap corroded a wire..then it's your dime to fix it
Some tap the trailer connector harness as well
That one is real easy..

 

[MTMan]

@powerboatr Thanks so much for the info! This is what I like about these trucks. They have all of these hidden gems. What gauge wire did you use to run to the back? And what is an upfitter book? Is it online?

 

[powerboatr]

@powerboatr Thanks so much for the info! This is what I like about these trucks. They have all of these hidden gems. What gauge wire did you use to run to the back? And what is an upfitter book? Is it online?

Another member here shined the light on the hidden wire under hood
It used to be out back near trailer tow harness...
aduitors saved ford 50 cents in wire to stop running it all the way to the rear, where its....needed
18 gauge
Body builder book is at ford service website..takes some drilling down
Yes on line
It's also in the commercial vehicles section of ford service
When I get back I will add the link

https://www.fordpro.com/en-us/upfit/publications/

 

[MTMan]

In the past for other vehicles, I've ordered automotive grade wire for different projects. I've learned there are different insulations but not an expert in this area. Curious for those with expertise in this area what type of wire the topper brake wire would be made of.

https://nassaunationalcable.com/blo...jcPnhfF5bFwaNODUMkZIQnqbV-VSHk1MwfH0XdjOD73V0

 

[powerboatr]

In the past for other vehicles, I've ordered automotive grade wire for different projects. I've learned there are different insulations but not an expert in this area. Curious for those with expertise in this area what type of wire the topper brake wire would be made of.

https://nassaunationalcable.com/blo...jcPnhfF5bFwaNODUMkZIQnqbV-VSHk1MwfH0XdjOD73V0

For me..
I use wire that runs outside the vehicle, inside frame etc with the thicker insulation, to give it more chaffing protection, as well as tucking inside some convoluted plastic sheathing.

 

[MTMan]

Finally getting around to this with the weather improving and found the wire. It looks to be very small gauge. What is the black end on it? Is it just protecting it from grounding out or is it something else I've never seen? And is it necessary or a good idea to add an inline fuse? I need to buy some wire and figure out how much I should buy for the whole run length and some type of conduit to put it through if anyone has a recommendation.

 

[MTMan]

Finished this project up yesterday. I purchased 25 ft of wire loom and high temp GXL matching gray wire with the orange stripe. I used over 23 ft of it more than I expected so sure glad I bought enough. I discovered the black rubber end on the provided brake wire under the hood is probably just to protect the wire from grounding out. I didn't have to remove the air box to get to it but was able to feel it under the drivers mount and pull it out. I used marine grade butt connector to splice in the wire and a marine grade ring connector to ground the negative wire at the end of the frame. That factory wire is something like 22 or 24 gauge. Yikes! Zip ties and tesa tape where needed and routed it through the hole in the bed forward of the drivers tail lamp. Finished it up with a Deutsch connector at the end to mate up to the one I added to the topper. Non powerboost here but still requires truck on for 3rd brake light to work. Thanks again guys!

 

[TFC]

I recently went through this exercise with a twist. Thank you powerboatr for the info.

2021 F150 Platinum 3.5L eco boost + SmartCap topper.

The SmartCap came with a wiring harness that was meant to connect to the truck in two places: one at the drivers side footwell to oem existing plugs and another at the fuse panel at the passenger side footwell. The harness is meant to go through the drivers side floor (existing grommet) and back to the rear of the truck to eventually plug in to the topper.

Problem was that my particular truck did not have the factory plug that SmartCap was expecting. I took two different attempts and a lot of body contortions to finally confirm that my truck just did not have the factory connection that their harness needed.

After a ton of internet probing, I learned about the CHMSL wire that powerboatr provided a picture of. So, at SmartCap's request (and on their dime) I took my truck to the Ford dealer and said please connect my topper's 3rd brake light. The funny thing is that the dealer said "we've never heard of that" and that Ford's technical materials "don't mention that" either. As an alternative, the dealer wanted over $1,000 to establish a connection through my interior and the headliner to connect to the truck's third brake light. Seemed excessive and SmartCap wouldn't approve the expense anyway. I don't blame them.

So I went back home, researched a tad bit more, and did it myself. Couldn't have been simpler in the end. I used the shielded wiring that SmartCap provided. I have a bedrug and pulled the carpet back a bit at the rear tailgate / bedrail to expose an existing hole that drops down inside the rear fender (i.e., I did not go through the taillight housing). As soon as I could, I started fishing the wire through the frame rail until I got to the engine compartment and then up from there.

I grounded in the engine bay and connected to that thin CHMSL wire. Brake light on the topper works!

Slightly strange part is that the topper brake light likes to subtly flash a bit when the truck is turned off. It lasts a couple of minutes and eventually turns off. I don't worry about it.

I told SmartCap they were going through a lot of hassle (and expense) by not leveraging off of Ford's provided CHMSL wire and creating a whole wire loom that needed to go from interior to exterior of the truck.

btw, powerboatr mentioned this but it bears repeating. Some models (or, perhaps different model years) have the CHMSL wire under the rear bumper coming off the trailer wiring harness (honestly that location makes a lot more sense than by the air filter...at least to me). So, you might have to hunt for your CHMSL wire a bit.

Good luck!

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