I'm think my next plan of action is to abandon the stock wire runs from the head unit to the amp that I recycled, and run all new wires. That way I'll know theres nothing between them messing up the signal.
Fortunately its a small car and the wire runs are fairly accessible.
Guess its gonna be another bloody knuckle weekend.

Z~
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...all I ask is a tall ship and a star to steer her by.