[fun in dirt]

Several years ago, in our 2001 Suburban, replaced the factory radio with Alpine 145BT receiver & new door speakers (Kenwood or Fosgates can't remember). Alpine is plugged into factory harness & I plugged in a bypass adapter for the factory amp.
At first the rear door speakers did not work ... but I had also taken out all seats & center console (with rear seat radio controls & headphone jacks) to replace the carpet and realized never plugged console harness back in. As soon as plugged it up, the rear speakers worked and did for the several years.
Then about year ago the right rear quit working, lazy & never investigated. But now the left rear has quit & I only have front speakers. Yesterday the passenger door is going in & out ... gotta fix this!
I have checked center console plug & all looks good; wiggled wires around there & at amp bypass plug with radio on & nothing happened.

How does center console controls tie into rear door speakers & factory harness? I would really like to eliminate this loop, as that doesn't control anything anymore since have the Alpine in now.

I know how to check speakers with AA battery to make sure they're good, but how do I check at wire to make sure they are getting signal from receiver?