dash light problems

I was installing a new head unit last night on my 96 GLS. I had to cut out the bracket that was behind the stock radio in order to make it fit. There was thin brown wire connected to that bracket with a female clip. At first I thought that that was the ground for the radio, but I saw in the harness that the ground for the radio was tan and thicker. I drilled a hole on the metal that the bracket was attached to and reattached the thin brown wire just in case. I had to pull the HVAC panel (vent,temp, and fan)to get behind the radio and clear the wiring harness out of the way. I also used the crutchfield harness adapter to ensure that I did not cross anything up. After I got it all back together the radio worked fine. I noticed that light that lights up the HVAC panel was no longer lit. I took it apart again and noticed that the place where the light should be had a thin grey and a thin brown wire going to it. Could it be that the brown wire is the ground, and I reattached it behind the radio the wrong way? How would I go about diagnosing the problem?

Thanks