I took it upon myself to try a photocell from a salvage Riv. It didn't work but was showing a different range on the diagnostics. The highest I could get this new photocell was 56 which apparently was not enough to put the car in night mode. I really didn't want to put the dash back together until I had a fix for the problem. On a whim, I decided to try the Photocell from a replacement photocell used for 120v 300 watt outdoor lights. (Home Depot, .90, UPC 046335834811)

The photocell in the Buick is housed in a plastic holder that pops into place like a light bulb and when removed from this housing and replaced with a new photocell works perfect. The only downside is that it works too well and not only must you break off the blue top of the holder to let in enough light (the dash is dark enough during the day to trip it) and when it is dark the reading is higher than it needs to be so it will trip the B119 error code (photocell circuit error) but it wont hurt anything and works great!

Just be careful when pulling apart the dash. (center grill comes out first, three torx screws, and seven metal pull clips on the front (side closest to seats) should be lifted with a L shaped to to remove straight up to avoid cracking the dash)

Just so everyone knows, the reading in the BCM data for photocell must read 74 or more to put car into night mode.