Ok I have an 86 turbo with the digi dash. It doesn't work for crap speedo reads 0 all the time and the gas meter is only on when I am above half a tank. Boost water temp and oil are all unlit.

What can I do ...? Also is there any way to go to an analog dash ?
I have one sitting around any one have similar problems?

speed sensor is in front of the battery on the passenger side strut tower. clean the cable and replace the two seals at the transmission end. then replace or clean the sensor.

fuel level sensors are notorious for going bad. analog or digital, it doesn't matter. replace it. you can get to it from under the rear hatch carpet through the access panel.

to fix the last problem, you'll have to open up the instrument cluster and find the fried FET. Once you replace it, those gauges should work again.

yes, you can go to an analog dash, but it would probably be a little more work as you have to replace the dash harness requiring removal of the dashboard.

If you need a new fuel gauge, check with Steveb10 on Ebay. He is always selling parts on Ebay for Z31's, and he has a lot of digital fuel gauges he sells. I have purchased about six or so items off him, and he always delivers.
About converting to an analog dash, thats going to be more trouble than its worth, in my opinion.