If the heavy battery connection is on to the starter, then put the extra wire from the battery +ve to the small wire on the starter. The starter will jump into like and turn the engine over.
Or if the starter is out, put the body against the battery -ve post and use a heavy wire, or jump lead to hook up the +ve.
When you turn the key to start, all that does is put 12v on the small starter wire while you hold it in the 'start' position.
