I know the moderaters are probley going to get mad at me for this but Im not asking about painting just some tips on preping the car. Anywho, I just called Maaco and decided to get a supreme paint job for around $500. They said if I could prep the car myself then i could save about $130. So I started to sand the car down with 400 grit sand paper when i realized that I have no clue what im doin. I know that I have to sand or scuff the car up for the paint to stick, but how far down? Also the paint on the front bumper is already down to I guess the fiberglass, (its yellow), so do I sand the whole bumper to match it?? Or should I just bondo over the spots and sand that down? Some parts on the car, the clearcoat is all gone but like on the rear of the car and the hood and perfectly fine. Any tips or feedback will be fine and appreciated O and its a 89 240sx sedan bought last week for $750 (runs fine)

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I had the same question put yesterday in another forums. Lemme direct you to it.
http://www.anteaterforum.com/showthread.php?t=12890
One of the guys actually repainted his hood with rattle cans and it came out very good. Pay attention to phidong's replies more.