On my 77 I'm not sure if my temperature gauge inside the car is working properly.  After running it and when the engine is warm the temp. gauge seems to not be moving at all.  I am concerned that if this gauge is not working properly, I may overheat the engine accidentally and cause damage to it.  How can I troubleshoot or check to see if the gauge is working?  Thanks again for the help!

Take the wire off of the sending unit, on the side of the head(driver side, normally), and ground it to the engine somewhere. With the key on, the temp gauge should peg out. If it does not, there is a break in the wire from the sending unit, or a problem with the gauge, or cluster contacts.
If it does peg the gauge, the sending unit is not functioning. The connector may just be loose on the sender, also. Sometimes the terminal gets a bit spread out, and just doesn't make good contact.