first off please don't use a battery to test for speakers; you only use them to test phase. if you get the wrong wire you can cause damage or possibly set off an airbag and injure yourself (i've seen it happen). Always use a meter to test wiring. voltage for power wires and resistance for speakers.
do you know what wires you connected to? in the ford harness there are two wires that will appear to be a ground if not tested properly and can cause weird reactions if connected to the wrong one. i do have schematics on what the stock wiring is for comparison. also what brand and model is the unit you are using? certain ones have different non-cea wiring colors and can be easily confused and mixed up. grounding the parking break wire shouldn't cause any issues.
also the adapter you were looking for is one that will connect to the car's factory harness and have open ends that you can then splice to the aftermarket headunit's harness.
2010 Volvo C70
2011 Harley FLHTK
Midwest Crew #22