One possibility is that the starter may have the wrong drive installed, it has to be set up as positive ground to engage the engine but it doesn't have enough power to turn over the engine.
I'm guessing it has a motor wound to have maximum torque in a negative ground setup but, has a drive that engages in the opposite direction.
If I hook it up with negative ground the starter motor spins freely because the clutch in the drive is being turned the wrong direction.
Is there something I could be missing? I'm jumping it with the dual batteries from my diesel, and 4ga. booster cables so I think I'm getting enough power, I've also tried multiple ground points including right on the but of the starter so I should be getting a good ground.
The truck is an early 40's Chevy COE.
