just had a quick read of your saph issues. it appears to have all the hallmarks of earth problems.
although there are lot of failures and poor voltage, try to sort out the simplest one first and it may lead to a better conclusion and the reasons for the rest.
i would look at the oil light first as its very simple. according to your measurements from the connector behind the dash you have 2.3 volts, but were did you earth the meter.i would sugest you earth the meter directly to the battery negative terminal to see if there is full continuity, or just earth the oil switch connecter direct to the battery neg terminal. if it lights or you get the 12 or so volts then you know where to start looking.

if there is 12v at fuse 22 and at b/y wire a the connector at the clocks then only an earth from the engine or the looms can cause the rest
see how you get on with the above and we can go through each system step by step, i have a full set of saph 2wd and 4wd wire diagrams and they have been very accurate and helpfull in the past to other members