I had the same type of questions when trying to install a radio.  I 
took said radio to a local radio installer and asked them.  Very 
friendly and offered some advice.  Turns out on some of the newer 
equipment has to "pull" power rather than be "fed" as we usually 
do.  I has something to do with having a separate pwer supply or amp 
or something, anyway if in doubt have a pro look a your particular 
installation.  Same with speakers, more money  = more wires ! ?
- Jeff

> Date:          28-Jul-1996 14:29:01 -0500
>> I figured this would be a simple hook up of existing wires but I've run into
> some unidentifiable wires.  For example, my radio has one red wire for power
> but when I look at the hot wire from the van it is three wires leading into a
> wire harness.  What might three wires be doing here?  Is one of them a
> neutral, the other a ground, etc.?  Or are the other two here for moral
> support?  Can I simply wire all 3 together into the red one?  Also, the
> speakers have two wires each coming from the van and the radio has, of
> course, only one for each speaker.  I originally thought this was a ground
> for each speaker but someone said this could be a "+" and "-" connection.
> Rich