electrical woes

[youda]

first question is what would cause the fuel and temp gauge to run fine for a while then both max out with both needles going all the way to the right after about five minutes of driving?

second is will disconecting egr stuff ie fuel cannister throw a engine warning light up?
the reason i ask this is because my engine light is always on but the car is running fine. the only thing i have disconnected temporarily is that.