Driver side speakers fade in and out

Pull speakers and test one by one.

Check the speakers if they work. Connect the speaker terminals using a short wire to a 1.5 volt battery (AA or any dry cell batter) and listen if there's a thumping sound when the wires are connected to the battery terminals. If there's no sound, your speakers are busted. If there's a sound, check if the wires are okay. Use the same method with the battery with the wires from the back of your stereo. Make a small cut on the wire and attach the short wires you used earlier.

The most common solution is both rear speakers are bad. Not what you expect, but is what we usually find. could be a driver in the radio.
Go back to the rear speaker and put your ear right on the speaker and notice if there is a faint sound.
Have a test speaker and plug up before you buy the correct ones.

Amplifier gone or wires loose. Try disconnecting battery for ten min ,can reset unit.

There is no fuse to the speakers your rear speaker wires should run under the kick plateon drivers side broken or disconnected wire or burned out channel in radio.

Did you maybe bump the fader button so that all sound is faded to the front? That's pretty easy to do.

unfortunately there is no way to "fix" that particular issue. the switch needs to be replaced.

Your front speakers are more than likely blown. They make all kinds of different models and price ranges to look at. This gives you a good opportunity to upgrade your stock speakers to handle what your throwing at it.

check the connection atr the back if their ok or maybe you just have a loose wire on it...

are youre balence and fade settings in the middle?