Third brake light wiring question

[Pablo M]

1972 2002tii

I'm installing a third brake light. 
I see the wiring bundle on drivers side in trunk. I thinking I’d tap into the green/red wire for power and brown/yellow for ground. I didn’t get clarity from the wiring diagram I have. 
 

Does this seem right? 

[tzei]

Br/y does not sound right. Plain brown is usually ground. I have made separate ground to chassis for 3rd brake light.

[visionaut]

On my square, I tapped green wire and brown wire along the right side…

Edited June 7 by visionaut
clarity

[bergie33]

Put a volt meter on it at the back of the brake light and have someone step on the brakes.  That should tell you if you have the correct wire.

[zambo]

The green/red goes to brake switch on a ‘73 onward model diagram.
 

Not seeing the brown/yellow in the trunk bundle on this diagram but the elec diagrams aren’t always totally correct 🤔. 
 

Karl’s suggestion above puts it beyond doubt though if you have an assistant or even a stick to depress the brake pedal so you can check. A house painters extendable pole works great. 

Edited June 7 by zambo

[Lucky 7]

That brown/yellow is your fuel level sender, don’t tap into that.  Green/red is your brake light, though. Everything in the trunk grounds to frame in the corner, so I’m pretty sure you don’t even have a ground in that bundle to the trunk. I just ran my third brake light ground to frame…I sank a sheet metal screw on the C pillar.  

[jimk]

Just look at the wire connected to the brake light bulb!

Edited June 7 by jimk

[Son of Marty]

6 minutes ago, jimk said:

Just look at the wire connected to the brake light bulb!

The colors mean something 🤯.

[ray_]

1 hour ago, jimk said:

Just look at the wire connected to the brake light bulb!

I just teed off the terminal on the taillight housing rather than hacking the harness (in this case).

[visionaut]

3 minutes ago, ray_ said:

I just teed off the terminal on the taillight housing rather than hacking the harness (in this case).

Me too. (why I can haz brown) 😁

[John76]

24 minutes ago, ray_ said:

I just teed off the terminal on the taillight housing rather than hacking the harness

+1 Ray!

Find the brake light bulb in your roundie and connect to the + and ground (you can ground your 3rd. light anywhere).

Here's how I did it on the passenger side square-light.

 

 

 

[Pablo M]

The multi color brown threw me for a loop. I knew it wasn't right for a ground. I was trying to keep the new wire length short and not have to go all the way back to the taillight. Taillights ground in the middle behind the brace so I can't see them easily, or access them as they're bundled up in tape. 

My wiring diagram doesnt show my side marker lights either, which I see are grounded to two brown wires. Again, I was hoping to keep the wiring to a minimum. And I didn't want to drill a new hole to do a new ground. 

Looks like I'm extending the wiring to the taillights and grounding to new chassis ground...

[John76]

12 hours ago, Pablo M said:

I'm extending the wiring to the taillights

Pablo,

You only need to attach the + wire from the new 3rd light to only 1 taillight.

Here's the connection for the side marker light and ground wire.

 

 

 

[JQ02]

@Pablo M do you mind sharing a pic of the finished brakelight? 

I'm curious what light you went with and where you got it?

Thanks

[Pablo M]

11 hours ago, JQ02 said:

@Pablo M do you mind sharing a pic of the finished brakelight? 

I'm curious what light you went with and where you got it?

Thanks

Sure thing. It was one of the lights someone here used. I picked it up from a previous thread. 
It’s this one (no longer available, but for information only): https://www.amazon.com/gp/aw/d/B076F4Y98W?psc=1&ref=ppx_pop_mob_b_asin_title

 

It matches the slope of the glass very well. I also have a thin LED strip I was thinking of using. It would have been more stealth but needed to figure out mounting. This one self adheres to glass. Does the job, doesn’t look too bad.