I am installing a newer Ford premium CD player in my 1990 limited edition Mustang convertible. Issue is the factory amp in the car uses a common ground. There are five wires from the head unit to the amp. The newer head unit from a Probe uses the gray data cable that has a +- for all speakers or 8 wires. Can I just use one of the grounds from the newer head unit or connect all of them to the one wire that goes to the amp?