Installing Or Replacing A Car Stereo Receiver (also known as a "head unit")
MOST IMPORTANT! Receivers can be very different! Read the instructions that came with your unit. They will usually identify the wires and their connections, as well as contain special instructions. This information may be on one of the unit covers as well. The unit wiring colors will differ from the car's own wiring scheme.
TOOLS YOU WILL NEED: wire strippers, pliers, screwdrivers, wire crimpers and wire nuts, 12-volt light tester* or, preferably, a Volt-OhmMeter, and electrical tape. (*Newer cars have extensive internal electronics that might be damaged if a light tester is used.) See a complete suggested tool list here.
BE VERY, VERY, CAREFUL! The slightest slip may short circuit connections in the underdash area that is often densely packed with electrical devices. Such damage could be expensive.
1) Remove the old receiver. Notice that it has a ground wire, a 12-volt electrical power wire, and four or eight speaker wires. It may also have Connections for line inputs and outputs for other devices like a CD changer, and/or power amplifier. Consulting the instructions of schematic, note carefully the identity of each wire on a small piece of paper, which can then be taped to the appropriate wire. The main wires should easily unplug from the back of the old stereo. Almost every receiver will have it's own peculiar plug, necessitating the removal of the old plug, and the connection of all the wires to the new plug on the back of the unit.
Do not connect the main power cable, until all other connections are made!
2) Connect the positive [+] wire from each speaker to the positive terminal or wire end, on the back of the unit. If connecting wire to wire, be sure to strip each end of insulation leaving about 3/8ths inch of exposed conductor on each end. Twist them together, and then screw a wire nut over the connection making sure that no metal in the wire is exposed. Tape over with electrical tape.
3) Connect the negative wire [-] from each speaker to the negative connection on the back of the unit. Follow the procedure outlined above.
4) Connect the ground wire of the stereo to a screw or bolt near where the radio is mounted in the dash. Make sure the wire is attached to metal frame part with a known good electrical connection to the battery negative. Do not attach to plastic or fiberglass parts.
5) With the ignition off completely, pull the 12-volt constant voltage wire from the cigarette lighter. Use the VOM* or test light to be certain you are selecting the right wire; the light will go on if you have tapped into the 12-volt constant.
6) Connect the constant voltage lead from the receiver to the 12-volt constant. Connecting the constant lead ensures that the stereo's built-in clock and memory features always have power.
7) Find the ignition source. Turn on the ignition and select the wire from under the dash. (An auto-repair manual such as "Chilton's" can help you identify the appropriate wire.)
8) Pierce the wire with the VOM or light tester* probe. The light will go on if you have the correct wire. To assure the accuracy of your selection, turn on the headlights; the tester should continue to shine with the same intensity.
9) Connect the "turn on lead" from the radio to the ignition source.
10) Look for more electrical leads coming from the receiver. These leads make power available when the unit is on and can be used to operate a power antenna and/or amplifier. If you don't have these items, cut off any exposed wire end part and wrap the leads with black electrical tape so that they do not touch a metal surface and short out.
11) Connect the line in and line out RCA stereo cables to the appropriate devices, Amplifier and CD player, usually.
12) The remaining plug is for the antenna. Connect it to the car's antenna line.
13) Find the metal brace that comes with some units. Mount the brace to the back of the stereo and to a secure surface under the dashboard. Attach the faceplate to the dashboard. Put the knobs, if any, on the appropriate shafts of the unit.
14) If there is only one wire coming from the speakers, the speakers are grounded at the car chassis. In this case, you may need to install new speaker wiring, if your receiver requires electrical isolation of each speaker.