brake light switch

[Pop's Ram]

I will be towing my Laramie behind my Class A motorhome, and the braking system I'm using (Demco's Stay-In-Play Duo) came with an indicator light to let me know when the braking unit activates - I'll see it in the RV's rear camera. It needs to tie into the brake light switch in the truck, the "cold" side that only sees 12V when the brake pedal is pushed. Any ideas where I can find that switch/wire? I do NOT want to disassemble the dashboard to get at it, so I'm hoping that someone can point me in the right direction as to where I can tap into. Or, is there somewhere under the hood that I can tap into?

Thanks in advance!