Stuart, the oil pressure is definitely yellow with a black stripe to no. 18, the junction block to gauge are internal to the instrument cluster. I found another anomaly when putting my S2 together recently, the connector block you have pointed out no. 42 had all positions populated, but the top right pin which is shown as blank had wires connected as a joint only, the is no corresponding pin on the back of the gauges. The red black wires go to the alternator, or at least one does. I part of spare loom here if you want some photos.
Neil
Thanks Neil. I am currently working through the loom to compare what I have on my loom to what the drawing says. I haven't got as far as looking at junction block 42 yet, but will have a closer look at it when I get that far! No doubt I will have a few more questions when I have finished comparing my loom to the drawings