2004 Ford Taurus • 83,000 miles

Ever since I installed a sound system in the car (nothing over the top) the following 3 things have happening. 1 my thermastat guage shows my temp higher than usual. For example when the car has cooled down over night and turn on car immediately the guage goes up a bit as if saying the car is still warm and when it reaches normal temp it is over the half mark showing that it is running hotter. 2 my fuel guage shows me at 62 miles left to E and it still shows me at more than a quarter tank left. 3rd just started recently my driver door ajar prompt comes up on my dash and I hear a clicking noise on the dashboard. I have tried to clean the switch on the door but so far no change. Any suggestions on these issues would be helpful.
September 7, 2012.

Most likely you have a ground circuit not secure. Recheck the work on the sound system and check for loose ground circuits around the area.

Sep 7, 2012.
Sounds like you tied into a wire that is causing this havoc. Remove the radio wiring and see if all returns to normal. If it does, then you need to correct your wiring.