No sound front left channel - 2020 w/ Alpine

[Tjw]

Bought a used Bighorn 2020 with alpine system - stock speakers. Noticed issue with the front L door and front L dash speaker with no sound from time to time. Upgraded all front 5 speakers (2 doors, 3 dash) worked for a bit but now nothing on front left channel. Left it off the battery all night, did a radio reset, and a sirius xm radio reset. :/
This was an issue prior to any speaker replacement to be clear...
What is my best option to troubleshoot if this is the amp or head unit?

Thinking about getting the PAC amp pro unit and a new amp, but if the head unit is a problem, I need to know now.

thanks

 

[Dragonmaster13]

Had the same issue intermittently on my alpine system. There is a harness under the driver seat that wasn’t fully seated and locked in. Plugged it in and engaged the lock and haven’t had an issue since.

 

[Tjw]

I took a look at the harness connections on the factory amp and reseated them but no luck.
Havent gotten behind the radio yet...