NOOB questions sorry ahead of time.

[chad1966]

These Q's are for my 1982 265 D24 M46.
Ok this is my first volvo. I have 2 questions and searching really didn't help. My fuel gauge does not read past half (car has sat for 6 months prior to me purchasing it last Saturday. Are the gauges/senders the same for diesel and gas? What could be the culpret? 2nd I cleaned the contacts on both dome lights and they both turnon in 1 direction but only turn on sometimes regardless of the door open or closed in the other direction. They both turn off when switched in the center.
Thanks and I will probaly have many many more questions here in the very near future.