Shifter moves without applying brake

New rebuilt trans fyi, this was going on before I made the swap. Shifter does not move until I turn the key to battery-on position from there I am able to shift gears without applying the brake, and I dare not test if it still moves while in motion and the last thing I want to do is accidently nudge it somehow and tear up my new trans. Not sure what is associated with gear shifters or what keeps it locked..