He is not jumping the Starter, he is jumping the solinoid...and I assume you know the difference between amp draw of the primary solinoid circuit in camparison to the amp draw of a starter..

You a TECH ?????????????????????


... for original poster:
Do a Search On "X27 " ..that is the 3 wire terminal we use for starter circuit verification...there are many post on the subject. Wire size for jumper will be same as the center wire at the X27 terminal....it is the starter that requires a heavy cable , not the solinoid in this simple circuit test.