The amp harness just makes a big loop from the head unit down to the amp under the seat, and back to the radio area where it connects to the body harness.
You are just going to unplug these four ends of the amp harness and tuck them or remove it. After that, wire your radio directly into the body harness
You are only going to use the 70-1770. You wire your head units plug into the 70-1770 and that plugs directly into the body harness once you remove the amp harness.
71-1770 is to repair damaged factory wiring usually when someone cuts the factory connectors off and wires the radio direct
Audio/Visual Electronics - Foxbody Head Unit Install Amp Bypass - Thought I would throw up an FYI thread for this, since I had such a hard time and couldn't find anything definitive anywhere. I know some people are having trouble with this install, and it turned out to be rather straightforward...
You are only going to use the 70-1770. You wire your head units plug into the 70-1770 and that plugs directly into the body harness once you remove the amp harness.
71-1770 is to repair damaged factory wiring usually when someone cuts the factory connectors off and wires the radio direct