Connecting receivers or amplifiers wires must be connected correctly on both the receiver or amplifier and speakers. When there is a long cable run to be split to go to both speakers.

Connecting Multi Zone Speakers Sr5014
Connecting speakers to amp. Then that harness plugs into your car. Thats the bottom side of the triangle in the photo speaker wires from the amp connect to the speaker wires on the adapter harness. A bit beyond the standard stereo speakers are speakers that come with a subwoofer. I was reading your post on how to connect 4 speakers to 2 channel amp and about speaker selector switch. After connecting the cable follow your tvs and audio systems setup procedures. In this configuration its usually the subwoofer that connects directly to the console.
On the back of the stereo amp plug the speaker cable into the appropriate speaker output jacks. For us it is simple but the young generation never grew up with stereos and some need guidance. To connect a set of usb speakers or headphones insert the devices usb connector into one of your computers open usb ports as in the picture at right. Connect a digital optical cable to the digital optical output on your tv. Join the cables from both speakers to the cable from the amplifier. Connect the other end of the cable to a corresponding digital optical input on a soundbar home theater in a box system or home theater receiver.
Connecting speakers to a home audio amplifier place the speakers in the general areas of the room where they will reside. Speakers can also draw power from a subwoofer or from the pcs usb port. For additional information consult the user manual for your device. How to connect speakers is for some a difficult job but dont underestimate these same persons. Cut one wire near the 2nd speaker and connect the 2nd speaker in series with the cut wire. The device should be automatically recognized by the computer.
Of course you can connect multiple speakers to both the left and right amp of a stereo you just need to follow the principles twice once for each amp. Running the amps output wires to the wires on the adapter harness is how you avoid having to run new speaker wiring throughout the car. Speaker parameters impedance 4 ohm power 100w each speaker has impedance of 4 ohm. Multiple speakers on one amplifier by adding an extra speaker to the output of an amplifier you are adding to the load of the amplifier. The positive speaker terminal red on the receiver or amplifier must be connected to the positive terminal on the speakers and the same applies to the negative terminals on all the equipment. Make sure you can access the back of each speaker during setup.
The stereo speakers then connect to the subwoofer. Join the two speakers in series then join this to the feed cable. I am planning to use speaker selector switch. As far as i understand i will connect speaker a on my amp to speaker selector and connect all 4 speakers. Instead use speakers with a power adapter.