Nick,
Here are a few pictures from the tether repair I did to my CSS T-1. It should also be noted that the tether on the Reading T-1 and CSS T-1 were different from each other. The tether on the CSS T-1 is like MTH Proto series tethers.
The other thing I would do is use a multi-meter to trace and test each wire from the pin/receptacle to the board and make sure there is continuity at all four.
Since my issue ended up being the engine side, I used a slightly 'heavier' gauge wire than was originally installed. I also deleted the 90 degree shell on the receptacle. The wiring came from a computer sound board cable I had in my spare parts box.