That looks to me like you have found the issue. That green corrosion on the Negative (ground) wire will not be sufficient in trying to carry any significant current required to get the starter moving. Wiring and connections need to be clean and tight, sealed against water and air to prevent that crud from forming. The discolored copper shows arcing - most likely from a poor path and that bad connection.

Be sure to have both ends spotless when you put it all back together. Try adding some dielectric grease after you have connected the terminals and they are tight. That will help in the prevention of tis in the future.

 

Turns out to be the 19yr old ground wire from the battery to frame, got a set of 4 battery cables made for 25e, beats the OEM pricetag 😎

Anyways hope this thread helps whoever finds themselves in a similar situation down the line.
I guess what happened was the battery wire was so old and stiff, when I removed the old battery to get checked i pulled on something and snapped it internally so even after the new battery was installed there just wasn't a good enough connection like all you folks mentioned,

thanks for all the help and advice, only feeling that beats riding a harley is fixing one, glide on🤘