the buzzer you speak of is located in teh kickpannel of the driverside, pop that out and just see if its connected properly still there are two plugs one furthest away from the driver is black the closest one (shorter) is white.
gas gauge failure is not very common but does happen , however for various reasons, first one it could be the sensor has gone, or the actual gauge itself has gone, get a pro to look at that so your not pulling your hair out trying to figure that one out.
the taillight failure is gonna be one of three things (usually) either the bulb is burnt out, there is a short in the tailights or miss-connection or as stated above me the relay is starting to go.
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