'84-88 300ZX Digital Dash Fix!
Well this gets asked so much I decided to write a page about this for all the people with the digital dash blues. 99% of the time the problem is with the amplifier box that controls the display, not the head unit itself. The problem usually start out intermittent and progresses to failure.. It mostly affects the temp/fuel gauge cluster but can affect any part of the display depending on which pins are affected.
First off the amplifier is located under the lower dash cover on the drivers side. After removing this lower cover you can see the amplifier as a silver box to the right of the steering column. It's about 5X5 inches square. There are three 10mm headed bolts/nuts holding it in and two plugs into the top of it. After you get it out, remove the cover and you'll see the back of the board. The problem is the solder joints where the pins for the connectors attach to the board itself develop hairline cracks. All that needs to be done is to use some fine electronic solder and a small soldering iron and flow some new solder onto all of these joints.. After soldering just reinstall everything and enjoy your newly repaired digital dash display!
If this doesn't work (doubtful it won't, but have seen it) the amp itself is dead and suggest finding a used one AND resoldering it before installing as this is a very common problem. Anyway here's a picture of the problem area.
Picture by http://web.raex.com/~photo