I recently bought a 84’ z31 AE which happened to have a non-functional digital dash. After a lot of research I’ve tried all recommended repair options but nothing seems to work. None of the dash instruments come on even after messing with the cables. Everything seems to lead to the power supply being bad but even after resodering the connections it still doesn’t show a sign of life. I’m not very electrically knowledgeable. Maybe someone with this same issue has found a solution

 

I went to ebay and bought one. I tried all soldering like you..quite frustrating indeed! I even had to replace the entire dash panel..took the damn thing out fixed it then sold the car.

 

The only thing you can do is very slowly go through electrical testing every wire and solder joint until you find the problem. Power supply is where to look first of course.

My digital dash was having all kinds of problems (weird gauge fluctuations, flickering, gauges not working at all intermittently), and I very slowly went through and checked continuity and voltages across all wires and solder joints, as well as carefully looked at all joints. All connections, continuity and voltages lines up with the manual, and I found a few solder joints that were questionable. Re-soldered them and the whole digital dash has been working almost flawlessly for almost a year now.

Patience is a must with electrical diagnostics.