I have a kenwood kdc-x396, after install the left side channel "speakers" stopped playing the right side still works??

SOURCE: Kenwood kdc-mp528 amp/speaker problem???

This is a common mistake. This problem indicates that you are using the solid blue wire from the head unit to the remote turn-on on the amp. This is a power antenna wire that only receives power when on FM radio. You need to replace this with the Blue & White wire from the head unit (power control wire) to your remote turn-on on your amp. This should solve your issue.

SOURCE: Sound not coming from left side surround sound speaker or my right side front speaker

it is highly likely that you're TV is outputting mono sound, hence the left channel only. check your physical connections to the TV and the balance / channel volume on the television as well.

SOURCE: Kenwood Receiver KR-V127R - left channel not working

Select an input that is not connected, for example select CD with no cables going to the CD input on the backside. Will you then hear equal humming on both channels? If so, the amp stage is ok,
and the problem lies in the signal level circuitry.
Open the cover and use a plastic (insulated) stick to touch suspectible cables and components. When the sound returns, you've found the cause. Resolder or reseat the component/cable/card.
Use the insulated stick, NOT your fingers!

SOURCE: both left and right speakers play audio for right speaker

I think you mean the left channel is out but when you use test tone, the sound comes from left and right channels through the right channel speaker. If this is case, the switching IC is malfuncting. Unit needs service

SOURCE: Problems with int 5.1-Channel Home Theater Speaker System

yes u will need to chandge input jack from mono to stero radio shack $4 part u need y headphone splitter this should fix ur problem