The 2 wires on top of the motor plate run the park circuit and contacts are open when the cam pushes them apart. Sometime you have to clean the contacts if the motor doesn't park.
Without installing it, plug your spare motor into the bulkhead connector. Ground the case with a jumper cable or...
In place of the fusible put a bulb across it, such as a taillight bulb. It'll glow bright with a short. Start pulling plugs, wires or fuses till the light goes off. This will help you narrow down which circuit is shorted.
Don't ever run a wire to bypass the fusible link. It is your only...
Chamged firewall and cowl.
Did it on my convertible here: Weld up a bunch of braces first, to hold it all together.
http://www.cuda-challenger.com/cc/index.php?topic=44869.150
I had a used one that fit better than the new one, but went with the new metal anyway.
My 72 Cuda
Real BS-H code Cuda. 4-speed A/C disk brake car. Paid the equivalent of $400 for it but it was missing the drivetrain and a tree crushed the rear half. Had to do lots of metal work on it to get it to this point. Running and rolling.
Hope to get it running for my wife to drive one...