Truck Cap Third Brake Light Wiring Question

Hi guys,

I got a truck cap recently for a good price, and I'm looking to wire the third brake light into the left rear tail light wiring.

This is a picture of what is hanging down from the interior of the cap,

https://imgur.com/a/2Y0UMtC

I'm wondering which wires I should connect to which wires in my tail light?

I have a 2009 Tacoma Access Cab.

Any help is appreciated!

 

Yellow is likely ground for both the 3rd brake light and dome light. Apply 12V and see which of the other two wires lights up the dome and brake light respectively. For the dome light to function you'll need a wire fused back at the battery or tap the hot wire in the trailer plug if you have one. Someone else will have to help you with power ground wires to the stock brake lights.

 

Not concerned about the dome light of the cap as I have a gecko cap lighting kit on the way i'll wire seperately. Just looking to hook up the third brake light

 

Ok, you'll still need to figure out which of the separate wires goes to the third brake light.