Polaris 250 ATV battery connection there was no battery before only has one thick black wire at the battery holder is this positive or negative where does the other wire come from go?

The thick black wire is the negative which should be connected to the frame of the ATV (negative ground). The red wire comes from the battery positive terminal and should go to the start solenoid From the other side of start solenoid a red wire of the same size as the black one should go to the starter.