why people do this irks me, if you are going to cut the wires and splice why don't they cut on the harness side and splice there...
Cause, back in the old days when stock radios weren't worth anything, it was way easier to cut the plug off the old radio, splice it into your new Kraco AM FM Cassette CB radio, and plug it right back into the original harness. If you were really into your music, you'd do the same to the factory door speakers, then saw a huge hole or two in the original door panels for the Radio Shack speakers. ( Fastback owners were really lucky, they could also saw some holes in the side panels and folddown door and mount 4 more speakers....) Less mechanically inclined folks would just take a pair of home speakers and put them right on the back seat....
Please don't ask me how come I'm such an expert at screwing up rare parts......