Hi No.5,
I'll go with louma on this one. From your description, it sounds like a high amperage arcing in or on the starter. If I were you, I would unhook the battery first and then check for blackened areas where your red wire attaches to the battery. You may also see metal disfigured from the arcing. If nothing is on the outside and you feel adventurous, you might pull the starter apart and look for sparking damage inside. Just my 2 cents.
Dave