my first stereo

Hi I'm installing a Jensen stereo in my 1989 ford escort.  I got a wiring harness kit to use and am able to use the black plug part for the speakers but the power plug coming from the car is useless since somebody cut it away at some point.  The colors of the wires that were in the plug are yellow, green, blue and orange.  Can you help me find out what these wires do?  I also have been reading online on how to install stereos and it says to disconnect the battery.  I don't know much about cars but was wondering if I can safely touch the negative terminal.  The connector seems to be on there very tight and I may have to work at it to remove it.  Also it says on multiple sites that the ground wire should be be attached to something that is metal in the car and is attached to the body.  I have looked in the dash area and see a piece of metal which should work but there are no screws I can attach the wire to.  There are some holes where screws may have went but thats all.  Is there any other way I can attach the ground wire to that metal?  I hope you can help me out.  Thank You.

DJ

ok i dont have the program that tells me what color wire is wich but i am oing to give you an idea of how you can find out what wires do what. all you nead to power your radio is three wires power (+12) constant,  (+12) switched, and your ground  take a test light and check wich wire has a constant power and connect it to your yellow wire from your hu then take your test light and find the wire that has power only when you switch your ignition to on position that one goes to your red wire then just find your ground and connect it to your black wire you shoild allready have a ground wire in your  car harness and about you getting your ground from that pice of metal  in your dash you dont need to since you should allready have a ground in your harness and the other problem is that sometimes the pice of metal is attached to you dash (plastic) and there i no ground there.

hope that helps if i can ill get you the color of the wires later but if not you can still do it this way

ps: be careful when your doing this since you have to do it with your battery connected dont let the wires toch  

Wow.  Wish I would have found  that site before I started installing.  Probably would have saved me a lot of frustration and factory dash pieces.

Thanks all of you.  I'll see if I can get it working today.

did you get a good ground? if you have all the wires hooked up correctly then you might have a defect. just in case check on the radio itself or on the owners manual and you should have a wire diagram just verify that the wires are hooked up correctly