Car stereo wiring and L+ L- and GND

First, keep in mind that the concept of GND is really just a circuit common point. Any "common" is usually just one of the power supplies nodes.

A simple car stereo runs off the 12V power supply of the car. The minus side of the battery is connected to the car's chassis, and this is normally referred to as GND -- even though a car doesn't have a direct connect to the ground (unless you rip one of your tires off its wheel).

Without any fancy electronics (e.g., a switching power supply or an output transformer), the most that any given single amplifier output can deliver, with a 12V supply, is a signal with a 12V peak-to-peak voltage range. In older car stereo amplifiers, this 12V p-p signal was converted to a signal that would swing up (positive) 6V from GND and down (negative) 6V from GND via a simple series capacitor. Really cheesy (IMHO), and it limits the low frequency response of the amplifier/speaker combination.

Nowadays, two separate amplifier outputs are used for any given side. Two separate outputs for the left channel and two for the right. Each side's outputs are driven out-of-phase. The net result of this is that, if you connect the speaker between these two outputs (as opposed to one output and to GND), then you can get 24V p-p across each speaker. Even though this takes twice as many amplifiers (four total for stereo), you can take full advantage of the 12V supply that's available and (here's the real point) you can get up to four times the power, for a given speaker impedance. This configuration is commonly known as a "bridged" configuration. Even some home stereos use it.

So, that 's why there are two active outputs per channel. DO NOT ever connect one of the speaker leads to GND (chassis) in this configuration. You will, then, not be able to pass go, and you will not collect your $200.

Bob

Without seeing the wiring hook up, here is the best guess. YOu do not hook either speaker wire to ground. The + and - indicate the phasing of the signals. Speakers may (should) have marks on them also. This means that when the sound comes out of the speakers the voice coils move in the correct direction to reproduce the sound as it was recorded. If the speakers do not have the marks on them, you can do it yourself with a battery. Hook a small (low voltage) battery to the speaker terminals and see which way the cone moves. When two or more speakers are moving the same way, mark one terminal with a + and hook it to the + of the amplifier output.

Thank you very much for both responses. I am getting the hang of it.