I literally have the same issue I've since disconnected anything from the factory harness and i have no backlighting on any switch but the guage cluster and radio still dim and there are no bad fuses. Could it be a relay?
I have been trying to wire up a switch for my light bar on my 16 SR5 and its wired up and working i tried to jump the red from the Cali raised switch to the green on the wiper switch for backlighting and it only lit up the part of the switch that showed the light is on. Well i disconnected it...
