The neighbor has a TW35 II that the tach didn't work. Found that the wires close to the sensor on the pump were broken from vibration. Soldered new leads to the short wires that were left and then strain relief the wires so they would not vibrate.
Our TW30 brakes also seem to have to step them to the floor before they grab. Maybe the brakes are wore out. When the oil is cold there is a slight delay to when they activate. Maybe you have a leak in the valve body for the brakes as they are hydraulic assist.
I never had a TW35 dash apart but on our TW30 the copper fingers where the connections plug in get corroded. You have to be careful as they are really thin copper on the dash side and break easily. Not sure if the same setup is used on the 35 for the dash connections.
I'm glad there is not too much electrical crap on the TW30. Mechanical levers always work. How much cheaper would a tractor be without all the electronic crap that you really don't need?