Passenger brake light

Quick question! On my '73 challenger, all lights work except the passenger brake light won't brighten with brakes applied. Both sides light up with headlights on, but the passenger side doesn't light up with braking. Swapped the bulbs, recrimped questionable connectors in the trunk, etc and still nothing.

Also, wiring diagrams show these as 2 wire per, but I have 3. Looking for any advice, thanks
Author: Kuruton