Brake light on topper

On a newer or specifically 2020 Tundra is there any reason tapping the 3rd brake light on the topper into the drivers side brake light wouldn't work? Trying to figure out if I have a bad topper light which would be unlikely, or I need to tap the ground from the topper light to the ground on the drivers side brake light. Currently my topper ground is attached to a bolt on the sheet metal, and it is a verified ground to avoid messing with the truck wiring harness anymore than I have to.

 

That should work. What is it wired into currently?
The ground should work either way as well - connected to the ground wire or into the body of the truck

 

that's what I did. I did piggy back on driver side tail light both the ground and +. I used a posi tap. no issues to report.
Now when I added dedicated LED lights inside the camper, I did run +wire to battery and drilled hole on the sheet metal for the ground.

 

Thanks Guys. I ended up replacing the inline splice I used, then once I figured out whoever wired the light on the topper used the opposite colors of what one would typically use for positive and negative I got the light working. It's a Leer topper, and you can get a harness, I just can't seem to find the harness online. I'm debating whether to wire the dome light in the topper and call it good, or take it to a Leer dealer and have them wire the dome light and the auto topper unlock (unlocks topper when you use the remote to unlock the truck). Dome light is easy enough, but not sure how you wire for the synchronous unlock of the topper with the truck doors.

 

https://www.etrailer.com/Vehicle-Locks/Pop-and-Lock/PAL9772.html

 

You first should wire up the remote unlock for the tailgate, then you can piggy back those wires for the topper.

 

Ok, so I was wrong, the 3rd brake light works until the headlights turn on then it stops working. So has to be something with the fact it uses the same bulb for tail lights and brake lights. I have a 2020 tundra. Any other ideas on how to wire the topper brake light? If not I'll throw myself at the mercy of the Leer dealer since I can't seem to find the Leer harness that connects to the box in the topper. I'm trying to see if there is a spare connection in the fuse box for a brake light, but not really seeing anything.

 

You probably tapped the wrong wire on the bulb mine did that to I think

 

Probably sharing a ground with the caps dome light.
When one is on both will work.

 

The brake light on the topper works fine though during the day. Its only when the lights are on it stops working.

 

Ya you tapped the wrong wire on the bulb almost positive...can you take a pic of what one you did?

 

I have it taped up and sealed, but the bulb socket is labeled 1,2 and 3. 1 is a solid green wire, 2 is a white wire with a black tracer, and 3 is a solid blue wire. I'm tapped to the green as my positive, and blue as my ground. The thing is I took a test light, and the only wire that had voltage on it when the brake was being pressed is the green wire.

 

Mine goes green,white,red...
Neg to the white with black stipe and pos to my red in your case it would be blue.

swap your pos wire to your blue wire that should fix it. I believe I did what you I did pos to green first cuz I got power on my meter