So I've cleaned and tested a few things. First off, here is a link to a cleaned up wiring diagram on the inside of the contactor cover:

imgur.com/a/9ReVA (Copy and paste into browser address bar since I can't post a full URL link here)

I took apart and dried out the direction switch box pictured in that album, on the steering column. I also took apart and dried the brake switch (neither seemed wet, but still gave them a good shot of air).

I tested from terminal 13 on the terminal bar to the bottom (feed side) of the directional switch and get continuity when the brake is not depressed, open circuit when it is depressed which presumabaly breaks the contact, and this works as promised.

Under each contactor is a 4 terminal block that varies it's resistance depending on if the DS is in forward or reverse. If in Neutral, each measure 83 Ohms on the top right terminal, which drops to 40 Ohms if the respective direction is chosen on the DS.

I have no idea what resistance I should be seeing at each terminal except for the obvious GND and +ve closed circuits. I'm inclined to think something is wrong in these latches but no idea what and why both at the same time.

I can't seem to find this Master Switch that is referred to in the diagram, and I'm not sure how it would affect the operation anyway since I don't see any connections to the directional contactors.