"Common" lead to the door speaker and tweeter.. Now I'm no expert by any means.. but looking into tweeters for the corvette hookup.. the subject of ohms was brought up.. You might want to confer with Crutchfield on that subject..

Quick lesson I just looked up...


Significance

• Knowing about speaker ohms is important because it is a safety issue. Connecting too many speakers to a device such as an amplifier can result in overloading. When this happens, there is a risk that it may blow up. Amplifiers give their maximum power to the speaker when the impedance of the speaker is similar to the output impedance of the amplifier. If the speaker impedance is lower than the amplifier's, then the amplifier has the tendency to overheat. In the opposite situation when the speaker impedance is lower, the result is a poorer quality of sound.
  
  

Connections

• Speakers can be connected to each other in two methods: parallel and series. If the speakers are connected in a series, the impedances are added to each other. For example, two 8-ohm speakers in a series have a total impedance of 16 ohms. In cases where speakers of the same impedance are connected in a parallel, the total is the impedance of one speaker divided by how many speakers there are. For parallel connections of speakers with differing impedance levels, the total impedance is computed by multiplying the impedance of the speakers. The product is then divided by the sum of the speakers' impedance.