I just pulled my motors to install some new oil pan gaskets .and block off the oil bypass valve .To ensure we had no leaks we fired them up on the stand .Motors cranked right up , no leaks but only after disconnecting the alternator .Does this make sense ?Also had to disconnect one side of the coil .Im not sure why he did this but when the motors went in the boat neither engine has spark . I think he fried my ignition .

that make no sence how did you hook it up how did you run your ground, I have run many motors on the ground and never had any problems