Starting issue

You left the negative attached also? I suspect a bad battery. Thought it should crank on one. Maybe ones shorted out, causing problems. Maybe hook up only the new battery, along with jumper cables to a running vehicle. Let it sit about 10-15 minutes. See what happens. There’s a problem. Battery, cables, starter, somethings shorting the positive or causing a bad ground. Hot wire to frame would make ground wire overheat. So will ground shorting to positive, as in battery or starter.

 

Does the ground wire go from the battery to the starter or the frame? Columbia's had a frequent problem at the frame stud.
All kinds of special tools and equipment for testing this kind of stuff. Ever here of the KISS program? KEEP IT SIMPLE SAM! Get an old school test light with a light bulb ( 1889? ) in it. Connect it between the stud on the battery ground and a clean frame contact. Have someone try to start it. If it lights you have a problem. Frame to threaded stud on starter ground. Between ground studs between batteries.