Some may assume that a four-channel car receiver can only power a maximum of four speakers. However, you can wire multiple speakers to the same channel so that they share the same power. This type of speaker connection is called "wiring in parallel." Wiring six speakers to a four-channel amp is a simple process, requiring that you wire two pairs of speakers to the same channel.
Disconnect the negative terminal of the car battery for safety reasons and to prevent a short circuit.
Cut six lengths of speaker wire. Make sure they are at an adequate length to connect their corresponding speakers to the receiver.
Cut 3/8 of an inch of insulation off each end of each length of speaker wire.
Crimp spade connectors to one end of each of the six lengths of speaker wire. These spade connectors are what hook the speaker wire up to the terminals on the back of the speaker.
Connect each spade connector to one speaker's terminal. Each speaker should be connected to one length of speaker wire via spade connector by the end of this step.
Split the other end of each of the six lengths of speaker wire so that the positive and negative polarities are separated. It's important to match polarities when connecting the speaker wires to the receiver.
Decide how you would like your speakers set up in your vehicle. A four-channel receiver will have left and right front channels and left and right rear channels. Decide whether you would like to have four front speakers or four rear speakers. This varies depending on where you can wire speakers in your vehicle.
Connect two speakers to either the front or rear, depending on what you decided in Step 6. Connect your left speaker to the left channel by plugging the positive and negative polarities to their corresponding plug-ins. Do the same to the right channel with the other speaker.
Connect four speakers to the remaining two channels. Connect two speakers to the same channel by plugging the positive polarities of each speaker wire into the positive plug-in of the one channel. Do the same for the negative polarities. Repeat those steps for the remaining channel and two speakers.
Consult your receiver manual to ensure it can handle parallel wiring.