Try putting the jumper cable ground on the engine lifting lug and the other end on the cable to the ground lug on the shock tower. Do not connect 12v and see if it starts.

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Dave

'05 325xi
'10 E70 35d
'85 911 Carrera
'66 911 Work in progress
'91 Chevy C1500
'95 Jeep Cherokee
‘18 Jeep JLU