dash questions

i just replaced the gas tank on my friends 91 regal gs. he had a little incident with a rock, and basically the rock won. anyway, after puttin the new tank on, i turned the key on and off a few times to get the fuel pump working. everything worked fine, except for the fuel gage. it was on E, and then when i turned it on, it went to F, then past F, then way past F. He just went on vacation, so he hasn't been driving the car at all, so I dont even know wether the gage works or not. I'm guessing not, since i put about 30 miles on it, and it didn't budge. Any ideas on that?

Also, on the same car, his low fuel light randomly comes on and off, and same with the check gages. Any ideas?

Finally on that car, the dash light, that comes on when you have the headlights on, stays on even when the lights are off, then randomly shuts off, and with the opening of a door, goes back on. So hes just been taking the fuse out and putting it back on, i was just curious if there was a way to fix that one too so he doesnt have to deal with that.

And on an 89 Regal GS, the seatbelt light stays on, even when the seat belt is buckled. Any ideas on how to fix that one?