bought a new sony stereo today to replace the stock one in my 99 mercury cougar. finally figured out what most of the wires coming out need to be spliced to on the stereo input, but something is holding me up. there are a few wires that seemed to be duplicated, i.e. 2 seperate(?) black ground wires running to my previous head unit. now i only have 1 ground wire connected to my new unit, so do i attach it to both blacks (assuming the're both ground, they have identical coloring), or just pick one and hope it works?