scoony

I have an issue with my sound system. When I bought my 98 ES300 6 months ago only the front and trunk speakers worked. I figured it was a rear speaker and/or amp issue. Last week the front speakers stopped working, so I'm guessing it's an amp issue.

Anyway, i'm working off the following diagram:
https://www.clublexus.com/forums/3558924-post7.html

when i unplug jack B, the front speakers start working and the sub goes off. Plug it back in and the front speakers quit and the sub goes on. Is this just a bad amp? or do I have some weird wiring issue somewhere?

Thanks for your help.