Starter running with key off and changed negative battery cable

I have a 99 Ford F-150. I changed the negative
battery cable because I was told it had a
connection problem. I do so now when I put the
negative post on the battery the starter runs with
ignition off think it is silenoid. I don't think it is the
teeth or starter itself. I don't know where to start. I
had issues with truck all of a sudden not cranking
then I would tap post and it would start up and
also there was a loop ground that went back to the
same place on the starter on old ground.