Can you narrow it down at all?
For example, when you lose the gauges, do you lose all of them at the same time - speedo, revs, temp., oil, volts, fuel?
Or, when the speedo and fuel goes, do you still have the volts and oil pressure? I ask because the volts and oil are on a separate 'circuit' to the lower gauges and dials.. If you look carefully at the back of the unit you will see what I mean.
The gauges need power as well as a signal from the respective sender to work. This power is picked up from an electrical line on the flexible circuit board. Each gauge and each light bulb on the upper unit, for example,is drawing from a common line and connecting to earth via a common line.
There is a power feed and earth connection to the upper (volts/oil, associated lights) via the connector plug that clips into it. The lower (all the other stuff) has three plugs one of which supplies the power and earth connection. I did a diagram showing all the wires and their colours for each of the connectors on my 91 model. Send me a PM with email address and I will send you a copy. Might not be exactly same as yours but should be similar.
Both the upper and lower sections are fed from the same fuse on the main fuse board under the dash. So, if everything goes off, check the fuse and feed from there.
If the upper section of the instruments works whilst the other doesn't you can look just at the suspect section.
Then,on that dodgy section, if the gauges go off check whether the background lights (the ones that come on when you switch on the headlights) on that section still work. That will tell you whether power is getting to the section.
If power is getting to the section but not to individual gauges or bulbs it suggests breaks in the continuity on the flexible board. You could run jumper wires direct from a power source to the gauges or from the gauges to earth if that is the case.
