2010 Tundra brake light switch

I am going to use my Tundra as a "Toad" vehicle behind my motorhome and I need to splice in a "brake light relay" into the "Cold side" of the break switch. There is not much room to work under there so I am looking for which color wire am I looking for? I am no electrical wizard and one of the schematics I looked at it looks like the one labeled "BE" which I assume is Beige color????
Does anybody have a hints how to work in this area and cut and splice the wires??

Thanks

 

OK, can anyone tell me if the wires to the brake lights run under the left side sill.?? another thing, the wiring diagrams posted on this forum show the final connection wire to the brake light is RED when in fact it is green with red stripe. makes it hard to trace based on color

 

Look up trailer brake harness. I think the harness is behind the kick panel drivers side
Those posts may have information your looking for

 

ANOMIC..thanks for the tip. I forgot about that connection. Will check it out tomorrow when I get some time.