If you jumpered from bat + to center terminal of X27 w no crank, then the problem is at the starter/solinoid or a bad ground.[ assuming bat is up on charge]
Take a jumper cable and go from the bat - and go to a good engine ground
and retry with + to x27.

Also, take a good look at the wires going from the X27 to the starter [ behind oil filter]..common for those to have the same problem as the engine wire harness.

Suspect is starter.

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A Dalton