[SCWDP911]

My 17 yo son recently saved up and purchased a decent daily driver 85.5 944. Someone had already replaced the radio head unit with a Yamaha aftermarket one but it is a cassette unit and he bought a new bluetooth unit. Went to install and the wire colors all matched up to the Yamaha harness as far as ground, power, and continuous power. Here is the kicker - the old unit powers up and works, the new units will not(we have tried 2 different brands now because I was convinced the first one he bought had to be faulty out of the box). I have reconfirmed all new wiring traces back to appropriate factory wiring, though really had no doubt since the Yamaha unit does power on with no issue. I even looked to see if the new units had some sort of "remove me before installation" piece. What the heck am I missing here. Again, both red (factory green/yellow) and the Yellow (factory red/white) have 12v to the black (factory big red I believe). Help