Problem with 1994 Silhouette

I have a problem that I cannot find any info on in the service manual for this van. The HVAC controls no longer light up with the headlights turned on. I thought I had a burned out light, but when I changed out
the stereo, I also pulled out the HVAC control head, and there is no light. How did it light up? Is there a diode associated with the PC board that went out? I couldn't see anything that looked like it would light up on either of the PC boards. Is the only fix for this is to replace the HVAC head? This is really annoying when driving at night. In order to change a setting, I have to turn on the map lights, then attempt to read what I want to change it to.
BTW - I just bought this van a few months ago, and the buttons aren't even close to the other GM vehicles that I have (1996 Sub, 1994 Buick PA).
Any help would be greatly appreciated. If someone could point me to the section and/or page in the service manual that deals with this, I would be very appreciative.
TIA, Bill

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