you need a dash kit. go to your local stereo shop and they should stock the hyundia kit. any single din size stereo will fit.
http://www.modifiedlife.com/2003-hyundai-sonata-car-radio-stereo-audio-wiring-diagram/
you need to pop out the frame and unscrew the radio. You will need a wiring harness for an after market stereo.
The color codes for a 2007 Hyundai Sonata Stereo wiring harness are usually yellow pr green, red or brown, and black or blue. These different color codes are basically used for connection purposes.?æ
http://www.modifiedlife.com/request-a-hyundai-car-radio-stereo-wiring-diagram/
The wiring diagram has four wires. Brown wire for parking lights, green and yellow wire for for stop light and white wire for common ground.
http://www.modifiedlife.com/2005-hyundai-accent-car-stereo-radio-wiring-diagram/
http://www.modifiedlife.com/2001-hyundai-accent-car-stereo-radio-wiring-diagram/
its a 10 gallon usually
1 - 2 - 3 - 4 - 5
The 2005 Hyundai Accent is 5 ft. 5.7 in. (65.7 in.)100 watts stereo output wide.
This might help: http://www.carstereohelp.com/stereoremovalHyundaiExcel.htm
http://www.hyundaiforum.com/forum/showthread.php?t=6830