Freightliner won't shut off

Today I went to put the 4th battery in it was struggling to start in the cold with three new ones. I started to loosen the positive post. The ecm wire is on this post. As soon as I loosened the post a little the truck got power to it. The key was off. Hooked the forth up tightened the stud with the ecm wire the power shut down. It starts now fine like it has the last few days. Why would he power come on when the stud got loosened? Has me alittle confused.

 

I've debated that was thinking of naming it Christine. What could go wrong?

 

If anyone is reading this for answers. I’ve had this happen twice. Both times the ground for the ecm was broke off in the battery box. Reconnected it and problems went away.