Oldsmobile/Buick Repair: 1997 buick century custom, fuel gauge, buick century

Question
I have a couple of questions. First, my fuel gauge swings back and forth but normally stays near the full mark. What could cause this and how hard is it to get to, don't really want to have to totally drain and remove the tank. Second, the car runs great, have no problems starting or stalling however, when i put in in gear (normally this happens in reverse but occasionally in drive)I hear this clunk and for a split second the brake pedel drops a little, the lights dim.. inside and out. Its been doing this for over a year now, any ideas? Thanks

Answer
Hello Hun
The gas tank could be a bad ground wire off the tank and do no have to drop the tank to check that easy fix.

And the dimeing of lights is a bad reg in the alt .
have this changed and u will be fine .

By the way they are a nice car . Good luck to u hun and u have a pretty name pete