The disconnect of battery is OK but I do not undestand what turning on the key with the battery disconnected is going to do. There is no current available with the battery disconnected. Please explain.I would check the connector and make sure it is properly seated. With electronics sometimes (often) the fix is a cold reset. Disconnect the negative lead from the battery, then turn on the key. Let it sit for 5 minutes and turn the key back off before connecting the battery back again.