Hi GTi.Si
I had a No Spark - No Start situation which I fixed by simply cleaning the ECU plug. I now have an intermitant speedo and dodgy dip headlights which I am convinced is down to the big loom plug in the engine bay which I am going after this weekend. I have recently done the headlight loom replacement and the lights worked fine at the time. The car was left standing for a few days over xmas and the really cold period set in and all sorts of electrical gremlins appeared. The car had 4 to 5 inches of snow and a thick buildup of ice all over it. I have seen what happened to the ECU plug. I would bet that the big loom plug is subjected to the same oxidation and its shown to happen on the wiki pages as I found when looking at how to open up the loom plug. There are pics on there with what look like spider webs in the plug and socket so ...... **** happens !
They are not related to anything inside the car as I have been through the interior wiring recently after doing a heater matrix replacement.