Since my last post on the matter (MFA computer and Rev counter not working (but the digital clock is), and no oil warning lamp, most likely due to the battery being connected backwards, however speedo, alternator warning, indicators, headlamp lamp, fuel and temp gauges etc. all work fine), I've tried two more sets of second hand clocks. Both should have been working when I connected them into the car, but they didn't, showing exactly the same faults as the original set.
I've also had an autoelectrician to it, who was stumped. And I've tried the two sets of second hand clocks in a GTI Club bod's Golf Driver (90 spec with the same connector) and they worked even less than they did in my car - no digital clock. None of the clocks have looked knackered - no scortched bits, no magic smoke. I've ripped the first set to bits and there's nothing wrong with them as far as I can see externally.
I've also replaced the alternator since my last post.
It's looking very much like the signals coming down the wires to the instruments are in some way lacking, or that the car is blowing up clocks. Any pointers as to what kit I'd need to start checking this out (in particular, the rev counter feed which AFAIK is a pulse signal and hence I can't check up on with a multimeter would be helpful). Everything else is just a variable voltage from a sender as far as I can see.
My current thoughts are that either the rev counter feed is somehow not up to cop (however the autospark reckoned it all seemed fine), or that possibly there's not enough power going round as the battery's a bit weak.
Any ideas on where I should be starting?