Fuel/Temp Gauge Accurate w/Lights On...??

So my fuel and temperature gauges only work properly when the lights are on, regardless whether it's the parking or headlights but after awhile, both gauges go all the way to the max readings. When the lights aren't on, neither gauge reads accurately. Another weird thing is that when the lights are on, the right blinker light on the dash does not light up at all, but it works fine when the lights are off. Any suggestions?