gauges not reading correctly help

I am having some sort of electrical problem on my 2004. The temp gauge stopped going up to its normal position (now stays at the first line of temp scale when warmed up) and then a couple of days later when I filled up with fuel I noticed that the fuel gauge was reading low (never goes above 2/3 mark but goes down as the fuel is used). A week later and the check engine light comes on( #2 o2 sensor) and then goes out every once in a while. Just starting today the brake light that comes on when you pull the emergency brake won't go out when released, it stays on for about 3 min then goes out. I am thinking it has to be a grounding issue but have no idea how to track it down. Any thought would be appreciated.

Chuck