GMC 307 Dimming

I recently changed out a GMC 305 for a 307. Left the lighting bus inputs disconnected to allow the unit to dim using the photo cell. It gets too dark to see the labels, so I connected the lighting bus inputs to control it manually, but it doesn't have any effect, the photo cell still dims the unit and I can't bring it back to bright even with the lighting bus hi input connected to full bus voltage. Both the Hi and Lo bus pin inputs check out, everything else works as normal. Thoughts?

Hi Jim,

I sent you an email with some questions.

Thanks,
Steve