My RSI smartcap uses the hi mount wire. Initially wouldn't work until truck was started. I thought it should work off as well, but it didn't light up even though truck brake lights did. Seemed to need truck started for computer to recognize light.

DA

DA

 

Didn't try with the truck running tried just with the acc.on, have to try and start it and see if that works, thanks.
If that don't work I guess I will have to get a module to, not going to take it to the dealership for one wire,then see what else they mess up.

 

So it always has to be running, or just to "initialize" it?

 

Just to get the truck to recognize it for the 1st time.

DA

 

Figures, LOL!! I swear at one point I had it running, but can't say for 100% that I also had that wire hooked up
to the cap light. I think I was just looking for voltage from a meter.

I just looked at the 23 BBLB again. If there was a note in there about that, I didn't find it (and still can't).

 

I actually had it wired up 1st and tapped brakes with acc on. When it wouldn't work I took it apart and rewired it again. Next time I started truck after i tapped brakes again and the 3rd brake light wouldn't work and lo and behold it worked.

DA

 

Thanks guys for the info,wouldn't work at first left it hooked up for a day works great now,crazy it must have to figure out that it's wired in or something.

 

Problem Solved: I had this same problem with the LEER topper mounted third brake light not working on a 2024 F350. The topper installer said the purple "high mount stop" wire was inactive and I needed to bring the vehicle to the dealer for diagnosis. During the install, he was also having trouble getting the ground wire terminal to stay in the LEER wiring connector. As the installer was backing the truck out of the bay, the topper mounted stop light came on, which surprised us both. We tested it a few times by pressing the brake pedal and it worked as it should. However, after a few hundred miles of driving, I noticed that the dome light and stop light had both stopped working. I discovered that the ground wire was loose because the terminal was not staying in the connector. I fixed that problem by bending the tabs out on the ground terminal and reinserting it back into the connector. The dome light immediately worked though I still couldn't get the stop light to work. I checked all the connections to the "high mount stop" wire and used a 12v tester on the wire with the engine running and a block of wood holding the brake pedal down. Nothing seemed to work and the "high mount stop" wire remained dead. After leaving the truck alone for 30 minutes or so with all the topper wiring connected, the brake light came on as soon as I started the engine and tapped the brakes. This seems to indicate that the "high mount stop" wire has a sensing ability and is not active unless it senses that it is connected to a brake light and then only become active after cycling though starting the engine and tapping the brakes.

 

Currently struggling with this stupid CHMSL wire. Why is it a FET and not a regular fused or Hot when you apply the brake... Anyhow seems overly complicated to me. It doesn't help that I couldn't even test the wire since the truck has to be running and potentially it didn't "detect" the third brake light.

I have my 3rd brake light wired up and grounded to the chassis ground right near the spare and CHMSL wire. Tried it with the truck on, drove around and still nothing. Going to leave it overnight and see what happens.

On a side note, I have passenger front window bounce back and no matter what procedure of holding down and up I do to try and reset the auto close window, it never works. Maybe my BCM is shot...

​​

 

Just a word of warning, if you end up using one of the converters to generate a signal for your chmsl, watch the module very closely over the years. That was used on my last truck and eventually my light would come on randomly... Not long after this started, and I wish I was joking, my truck burned to the ground. I had surveillance video and could verify it started in the area where it was installed. No definitive confirmation as there wasn't enough of the truck left, but it was either that or something chewed on the wires around there.

It was a t-harness on the 7 way connector that came from Leer. And it was installed on a 2016 Chevy. It happened in the middle of the night, and because GM leaves the 7 way live all the time, I'm reasonably certain that's what happened. Ford may kill power to the 7 way, so maybe only an issue while driving?

My recommendation is to ALWAYS use the chmsl wire unless absolutely necessary.

 

I appreciate the input Andrew. Sorry to hear about your truck. I had considered one of those turn signal brake light tap modules if this CHMSL doesn't work. But I'll keep on trying getting it to work, given your experience with the add-on modules.

 

I never understood why it had to be "activated" in this manner. Real PIA going forward I think, trying to diagnose it if/when it effs up.

 

I have a 2017 F-250SD and just bought a used ARE Z-series topper for it. I've looked 3 times under the back of truck and cannot find the wire that is supposed to be there. I need help on figuring out how to wire this Topper to the brake, lock and unlock, and hot for its interior lights. Can't find much help on the wiring for F-250 anywhere. Thanks for any help or tips.