Originally Posted by BlueFireIce
Yes, checked harness for continuity, everything is fine. Checked speaker locations with a battery to make sure the diagram I had was right, it was.
The red and blue/white would be hooked up to the 10th pin (Constant Power) and 9th pin (Switched Power) on the harness.
Since we can now rule out any connection issue you may be experiencing an impedance issue. The easy fix is to use a High to Low level converter. Disconnect the High Level connections of the FAST-9999 and plug the RCA's of the BTAH into the converter installed.
If you are looking to purchase a aftermarket headunit you can skip this all together and connect the Tube using the Low Level outputs of the headunit.