If you're using an aftermarket radio, you'll need a pair of wires to each speaker, a positive and a negative. Generally speaking, the positive will either be marked with a red dot, other times it's a wider terminal. Keeping track of which is which with locally-bought speaker wire can be a hassle, but many places sell it with clear insulation where one conductor is copper-colored and the other is silver. I always used the copper as positive as an easy way to remember. Other sources sell it where one wire has a tracer, which I use for negative (personal choice) while others sell it with a constant row of marks, one positive and one negative.
Screwing up the polarity won't physically damage anything, but it definitely won't sound as good. Also, if you screw it up on one speaker and not the others, that speaker will be "out of phase" with the rest, hence cancelling out some of the sound. Make sure you get it right on all four corner speakers!
Luckily, aftermarket stereos have been using universal color coding on their wires since the 1980s. Not all colors are present on all stereos, but you'll
definitely have the following:
Red: 12V+, key-on/accessory. This can be wired to the original radio plug. It must be fused.
Black: Ground, usually with a screw lug on it. It can be connected anywhere there's a screw and good ground. It must be connected. DO NOT allow the stereo to ground through the antenna lead.
Yellow: 12V+, constant (battery). This can be connected to the clock lead if your dash has one, a "BAT" connection on the fust panel (also if present), or any fuse with a constant 12+ power source regardless of key position. This wire is both the main power lead and what maintains the radio station presets, clock, etc. Make sure this is a solid connection; don't just jam a wire behind a fuse. Buy a fuse tap if you must. The wire itself must be fused.
Blue: Power antenna, or remote turn-on for external amplifiers. Since you don't have either, simply tape off the end of this wire (unless it still has its factory insulated terminal, which is fine). This wire provides 12V+ (goes hot) when the radio is turned on, so it must not ground.
White: Left front speaker positive connection.
White with black tracer: Left front speaker negative connection.
Grey: Right front speaker positive connection.
Grey with black tracer: Right front speaker negative connection.
Green: Left rear speaker positive connection.
Green with black tracer: Left rear speaker negative connection.
Purple: Right rear speaker positive connection.
Purple with black tracer: Right rear speaker negative connection.
Other wires you may or may not have on the back of your radio:
Orange: Illumination. This will dim the radio's display when the headlamps (technically dash lighting) are on. It doesn't seem like a big deal, but it's like part-throttle kickdown: You'll hate it if you don't connect it. Modern stereo displays are friggin'
bright at night.
Orange with black tracer: Dimmer. This dims the display when the dash lighting is on, but will control that brightness with the dash panel dimmer. Very cool; also pretty uncommon.
Either of the orange wires (but not both) can be connected to the orange wire on the factory radio connector, or any orange wire behind the dash.
Blue with white tracer: Remote turn-on
for amplifers only. It cannot run a power antenna.
Use 16-gauge wire for everything. Leave all of the factory wiring (dash REAR SPEAKER knob, crossover box, etc.) out of the loop. Make sure none of the speaker wires will ground, either now or with use (avoid pinch or wear points). I usually run them under the sill plates, behind the kick and rear interior panels. Routing along the tunnel and under the rear seat seem convenient, but if someone sits back there bad things can happen. Radio go boom, or worse (overloaded electrical system: smoke, stench, fire etc.). You may never have anyone back there, but even kneeling on the seat for a minute while you're back there can lead to disaster, so run the wires along the side of the car.
The red and yellow wires must be fused, so if the inline fuse holders are missing they must be replaced and have the correct fuses installed. You can ignore this warning if your stereo is new and cool enough to have the fuses mounted in the back of the chassis (many do, I suspect yours might be one of 'em).
Now that I've explained everything's function, here's a lovely quick-reference chart so you can remember the wires quickly:
I would
highly suggest installing "bass blockers" inline between the stereo and the dash speakers. This will keep bass frequencies from reaching your front speakers and distorting the sound or damaging the speakers when you're cranking Springsteen on a warm summer's night. Any local car-audio shop should have 'em on-hand. You have options here:
Go to the local car-audio place and ask the man for "600 hertz bass blockers." They
should simply plug into the speaker wires (white and grey, no tracer) but if he just hands you a pair of bare nonpolarized capacitors (that's all they are), just solder 'em anywhere in the positive wire and heat-shrink 'em.
If online shopping is your deal,
Amazon (wire-in) and
Crutchfield (plug-in) both have 'em.
If you're truly a DIY kinda guy, just get
thesethese[/url] and put them in the positive leads. If you have a local electronics shop like a Frye's, you just need 68µF (microfarad) nonpolarized capacitors rated for at least 50V. That's literally all they are.
Yes, this is
technically what the OE crossover box accomplished, but it's rated for different-impedance speakers and the components are most likely leaking or otherwise damaged. Even if it was perfect, it wouldn't work correctly since factory speakers are either 10- or 16-ohm and your replacements are only 4.
So now you're wondering about the center speaker. Odds are you'll never miss it, and in 99% of cases I'd say just plug the hole with the original speaker, leave it disconnected, and call it good. Were a customer having me install a stereo in a 3-speaker dash back when I was doing this stuff professionally, that's what I would've done every time. Making a center speaker sound good with the two corner speakers involves quite a bit of fiddling with the wiring and it's by no means intuitive (nor does it seem to make sense electrically speaking). Best results also come from having three speakers of the same efficiency (loudness at the same volume setting) which I don't think is the case with your setup.
If you
insist, I'll post how to do it. I just don't think it's worth it, and in your case I think the center speaker would actually be considerably louder than the two corner speakers. It's larger and has multiple drivers, both of which usually make a speaker more efficient.
