Hi, first post here.
03 Suburban, 220xxx miles. New 2004 BCM (flashed to this car), new drivers window switch. All windows work except the rear passenger. When using the switch instead of trying to operate the rear pass window, all of the dash lights (gauges, HVAC illum) go out. It is only as long as the switch is held down, But also happens with the window lock button - windows locked = no illumination and 3 windows work. fuses all good. Doesn't happen with the other switches - crossed wire maybe??
Previous owner did a lot of audio work in it - some is suspect. Works without a key - that normal?
Front and rear A/C also doesn't work - heat blows fine. The rear A/C isn't connected but I have a new harness to connect it (prev owner cut most of the roof harness for some reason), brand new HVAC control module

Also, any suggestions for what to look out for or things to check/upgrade for an 03? I already have the corvette servo (not installed yet) and the accumulator and "conversion kit" for the harsh 1st gear shift, a CAI, brand new fuel pump is in, has older 4 pin T Case for some reason (don't need 4WD right now but I do know I need a different T case if want it), front SS brake lines, new plugs to go in, brand new cats, headers and O2 sensors, new brake rotors and pads, new upper control arms.
Did oil, going to flush coolant because prev owner filled it with yellow instead of DexCool,

Thanks