Seeing this is the place of sharing our experiences' to collectively gain wisdom
Here are a couple of electrical issues that I had. You can see in previous photos that I now have a SSS dash facia. I bought it second hand from Tokyo2you in Japan but I see that there are replicas out there now. I have now got full VDO instrumentation which brings its own challengers in making it fit and still look OEMish. I ended up cutting some of the plastic from the rear of it and fastening the gauges directly to the facia. Seems to work OK. The electrical problem started with the Tacho, it wouldn't work! After having it tested and found to be working OK I checked the tacho output from the ECU with an oscilloscope to see what the output was. The expected output waveform was there but only a couple of milli volts. As I have a Nistune daughter board fitted to the ECU so I contacted Pete Liebig. Pete was very heplfulll and gave me the advice I needed. This is the jem of wisdom that was not on my radar.
Regarding the tacho issue - do you have a pull-up resistor fitted to the signal? They use an open collector driver in the ECU, so you need a pull-up to 12V. Anywhere between 1K and 10K usually works. I use 4.7K as a rule. That is all that was needed. The second issue came recently with the new fuel tank sender. I had bought an in tank modular kit from EFI Hardware in Melbourne (they make a lot of good stuff) and bought a different VDO fuel gauge that matched the resistance given for the new sender. When I did a test run on the gauge it went backwards. If you google fuel gauge going backwards you will get heaps of stuff however none of it was any use. At first I thought it was a polarity problem but it wasn't. I found that the VDO fuel gauge uses a rheostat that heats up to move the needle so it doesn't make any difference which direction the current is flowing. As the sender resistance wiper is an arc shape , it couldn't be turned upside down. I eventually found the device in the photo, the Gauge Wizard. The output of the device can be programmed to change the current to the meter to be the opposite of the sender. Not the direction of current but the amount, so the meter now works perfect. Also another nifty thing it does, because the new fuel tank is not a uniform shape you can programme various way points. In practical terms you put the sender arm in various positions e.g empty, quarter, half, three quarters and full, each time pushing a series of buttons. So now it has a linear output. It also has anti slosh facilities for voltage based gauges that the VDO gauge doesn't need because of the rheostat.