For your cup holder, Im not going to be much help. It would be nice if you run across something in the way of installation instructions to let us know. Or if you want to take pics and do a write up yourself, that would be great too.
For the temperature sender.
Stand in front of your car, hood open (obviously). Look to your right and you will see the upper radiator hose. Trace that hose to the engine and it will be clamped to the thermostat housing. Once there, look directly under the thermostat housing and you should see a brass looking thing with a plug on it, 2 wire plug. That is you coolant temperature sending unit. Costs maybe $15 to replace.
I just replaced my boss's temperature sender in his Bonneville and its and easy thing to do. Just be sure to use some plumbers tape on the threads to seal them up real good. Obviously this is something you want to do after everything has cooled down too.
