Auto Amplifier, Clock and Radio LCD Dimming
 

I own a 1993 Nissan Maxima GXE 4DR Sports Car and am having trouble with the Auto Amplifier, Clock and Radio LCDs dimming out for no apparent reason. It's not like a lose wire, but more like a grounding problem somewhere? But then again, it could be a lose wire? The digital clock has a tendancy to gain 3-4 minutes a week. The diming problem is intermittant and varies in magnitude. Sometimes the clock, Auto Amp and Radio are completely dark and at other times part of each display is dimmer than other parts. The A/C operates fine although guessing at the "Mode" settings and "Temperature" setting can be annoying. Do I have a bad ground somewhere? I do have the 1993 Nissan Service Manual for my car. At times, I can crank up the car and everything is fine. The next instant I look down to see where the A/C is set and the displays are either non existant or extremely dim.
Many thanks for any help on this subject.