Dash Light Problems

Hello, my buddies 02 tacoma (single cab, 4wd, 4 banger 5 speed) has no back lighting in the dash board. He has tail lights (same circuit) and the back lighting for the HVAC controls still works and the dimmer still controls them. We removed the gauge cluster last weekend and not all of the bulbs were burnt out (we did not check them all since none were working). I was wondering if anyone has the wiring diagram for the lighting circuits and the instrument cluster. I am hoping to not have to pull out all the wiring to chase down the connections to pin check everything. He does have an aftermarket radio installed and it seems to have been a cut and splice job. The radio is also randomly flickering and dimming by itself.
I searched a few threads on the topic and nothing we found seemed to be much help. Most are about burnt out bulbs, installing LEDs, blown fuses.