Well, I've got a CD player ready to go in and I cannot figure out what wire goes to what. i have four wires under the dash- three are black and one is blue. I'm stumped. I have nothing to test the wires with, either. And to make things worse, I can't find my camera to take a picture to make my problem any clearer.
The blue wire likely has a red stripe on it. If so, it's for the dash light in the factory radio. Two of the black wires likely go to the speaker in the dash. The other is a switched 12 volt wire. Test lights don't cost much, I'd suggest getting one. Or, if you're feeling adventurous, twist the red and yellow wires from the head unit together and, with the key on and the head unit grounded, touch the red/yellow wires to each of the black wires until the head unit turns on. That is your switched 12 volt wire. You will need to run another wire that has constant 12 volts.
In a pinch you can make a test light out of a tail light socket that has the wires still attached. One wire will be ground [plastic push in style tail light socket ] and one will be hot. Just ground it to the dash and then try all the wires until you get one that lights the bulb.
You could just run new wires to the fuse block and then ground one, it would be on constant power bypassing the ignition but.... you need a test light to even do that, and it's kinda "jerry rigging" (term used in virginia)...
Ok, I'm slightly confused. So I need to add a wire to run the new unit? How do I add one to a fuse block? This is really my first time dealing with putting new things into an old car. I have a test light, to be clear but it crapped out.
The constant power wire keeps the memory for your clock and radio station presets on a modern stereo. If hooked to the original switched power, you would lose them everytime you turned the car off. A really easy way to get unswitched power is to use the lead that runs to the cigarette lighter. If you are going to still use the lighter socket as a power port, then splice into it and connect it right back up.
No, you dont HAVE to add a new wire, i was giving a fast fix for you. Since you dont know how to plug into a fuse block, i'd go with captain comets suggestion with the cigarette lighter. You could always take it to bestbuy or circuitcity or somewhere and get them to install it for you for free if you buy there stereo... just a thought.
