You must pull the cluster out. This is a fairly large job as the needles have to come off the gauges but it is quite doable if you are mechanically inclined. The lights must be de-soldered and re-soldered back into the cluster. We have a full procedure at our enthusiasts forum
www.trailvoy.com
Sounds like you need a new battery.
Dash lights are soldered in place on the board. If they are all out you may have a fuse out or the instrument cluster is gone.
How do you replace the dash lights on a 2004 Nissan Quest
The illumination lights are replaceable. You will need to remove the dash cluster to gain access to them.
The drain for the condenser may be clogged.
They are tied to either the brake lights or the tail lights.
The dash lighting is all wired into the cluster backing on these trucks. It is possible to desolder and resolder in new bulbs but it is fine work. To increase your knowledge of these trucks join our forum at www.trailvoy.com True enthusiasts website for the GMT360 platform trucks!
Check the dimmer setting for the dash lights. There should be a dial to adjust the brightness on the dash to the left of the steering wheel.
A double din unit will fit in the Trailblazer/Envoy platform vehicle however you will need adapters. If you are experimenting then you are best to let a pro do it.
Alternator is failing.
have your battery and alternator checked but first check to see if switch for your dash lights are just turned to dim
Look under the driver side dash, near the front. You will see the plug there.