Welcome to 2CarPros.
I'm not sure what you are saying. The heading says it tries to start without the key in it when you attach the ground cable. The post says it won't start with the key in it, so I'm not sure what is happening.
If the starter engages when you connect the battery (key out), then you are getting power to the s terminal on the starter. That is the smaller wire. That should only get power when the key is in the start position.
Since you just replaced the starter, are you sure the main cable to the starter direct from the battery (thick one) which is hot all the time isn't touching the wire to the s terminal? I attached a picture of the starting system schematic below and highlighted the two terminals I'm referring to. For the starter to engage, the key must be in the start position which sends power through the starter relay to terminal 50. Once it does, a plunger is electrically pulled to the left and the contact plate allows power to flow via terminal 30 to the starter motor, which then turns the engine. So, if the starter is turning with the key out, power is getting to terminal 50. It could be a short at the starter from the repairs.
Let me know what prompted you to replace the starter.
Saturday, July 20th, 2019 AT 11:02 PM