1994 M900 starter

Hi All
my M900's latest trick has me wondering...
She started and ran fine, but when I pulled in for fuel, about 5 miles on, the engine would not stop turning. eventually stalling it on the brakes, but it took ages! It also started making a tortured metal kinda noise. When I whipped the tank up, I found the live cable from the battery to starter was red hot and melting its solder in the terminal!

I'm guessing the starter has jammed and just keeps turning the motor when connected to the battery, but a wee voice in the back of my mind keeps saying its a Sprague issue which is all new to me .Either way, I have to remove the generator cover, so any advice on tools, techniques etc would be very helpful.

Thanks and enjoy the riding weather