Negative battery terminal sparking on contact

Or you have an no issue and items that have been off for a bit like stereo amp or radio are “on” when you reconnect. That initial hit to the capacitors will cause a spark. Your description is tough to understand because a negitive spark is not unusual but not like arc welding. If you have a welding type spark then you have issues.
My Dakota mini starter does not hit anywhere on my 273 in a 66 cuda.