This is a 2007 Avalanche LT. It is all factory original.The backup lights don't work. The switch was replaced with a new one from GM. The fuses
and lamps were checked and found to be OK. The wires look good.
Another thing to check is that the switch is adjusted properly. Here is a picture of what the switch looks like if it is the same as my 96 Sierra was, and on the inside of the switch you can see a little square block, that block slides for adjustment so that when it is in reverse the backup lights will be on.
Again I am not %100 sure if it is the same style of switch or even in the same location. I'd check on mine but it is currently in the shop. Hope this helps.