Speedometer and Fuel level gauge questions
 

What is the electrical deal on the back of the speedometer (has a two prong connector on it)? I just noticed that mine is broken. Can this be replaced separately?

I noticed that my low fuel light did not come on before I fueled up last time. So, today I swapped the high beam bulb and the low fuel bulb to see if it was just a bad bulb. I wasnt sure if the light was supposed to come on with the key- it did not. With the key on I reached up under the dash to wiggle the bulb a little to see if it had a bad connection. When I did this the fuel gauge went from 1/4 tank to the empty line. I tried wiggling it more and it didn't change. I checked the main connector and it was completely seated. Even when the needle dropped to empty the low fuel light didn't come on. And another concern is that I have read that the fuel tank should hold about 21 gallons, with 410 miles on the tank, the gauge reading just above "E", it only takes about 14.5 gallons. Not sure if I have a gauge issue and a sending unit issue?

Any help with these issues would be greatly appreciated.