The main 8-pin connector for the factory radio shown here shows constant power on pin #4 but turning the ignition to position 2 doesn’t power up pin #6 (illumination). There is a connector with 8-pin and the same coloured wires down by the fuse box and I am wondering if this has anything to do with my radio not functioning?

 

Were you able to find a solution to this? I having the same issue of 12V on pin#4 but nothing on pin#6 (with truck turned on). thank you sir

 

Illumination pin probably only powers on with the ignition AND the headlights/marker lights.

 

Or reverse ! When the pin that gets 12V while lights are on, the radio display panel dims. You want more light during day, less at night. In other words, display backlight is brighter by default until some pin gets the signal of being 'night time'

The schematic diagram can clarify it.