The fuel gage and lights are probably two separate issues.
For the fuel gage, you may want to remove the sender (in the fuel tank - if you're lucky, you can access the tank without removing it. Check the upper front side) and either clean it or replace it outright. Brake cleaner or electrical contact cleaner and a toothbrush can work well to clean it - the additives in fuel can lead to varnish buildup, which can screw things up.
I've not had to source a replacement, so I can't help you there. I can tell you, however, that you should not use a steel hammer (rubber, wood, rawhide, brass, or lead all work) and you should not use a steel rod (I prefer brass) to undo the lock ring - you do not want sparks anywhere near your fuel tank, especially while it's open! Consider yourself edified (you should have at least a plastic or rawhide mallet in your toolkit anyhow...)
The lights may be something rather more simple - you happened to have a couple of bulbs burn out. Replace those - Hell, replace all of them while you've got the IP out (the main illumination lamps should be #194, and the small indicator lamps are probably either #37 or #74. Check to be sure...)
